# Interface to Sloane On-Line Encyclopedia of Integer Sequences¶

To look up sequence A060843, type one of the following:

sage: sloane_sequence(60843)       # optional - internet
Searching Sloane's online database...
[60843, 'Busy Beaver problem: maximal number of steps that an n-state Turing machine can make on an initially blank tape before eventually halting.', [1, 6, 21, 107]]

sage: sloane_sequence("60843")     # optional - internet
Searching Sloane's online database...
[60843, 'Busy Beaver problem: maximal number of steps that an n-state Turing machine can make on an initially blank tape before eventually halting.', [1, 6, 21, 107]]

sage: sloane_sequence("060843")    # optional - internet
Searching Sloane's online database...
[60843, 'Busy Beaver problem: maximal number of steps that an n-state Turing machine can make on an initially blank tape before eventually halting.', [1, 6, 21, 107]]


Do not prefix an integer with a 0 or it will be interpreted in octal. Results are of the form [number, description, list], and invalid numbers will cause sloane_sequence to raise an ValueError exception:

sage: sloane_sequence('sage')     # optional - internet
Traceback (most recent call last):
...


To look up the sequence “2, 3, 5, 7”, simply put the numbers in a list. The second argument specifies that at most 2 results will be returned.

sage: sloane_find([2,3,5,7], 2)       # optional - internet
Searching Sloane's online database...
[[40, 'The prime numbers.', [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271]], [41, 'a(n) = number of partitions of n (the partition numbers).', [1, 1, 2, 3, 5, 7, 11, 15, 22, 30, 42, 56, 77, 101, 135, 176, 231, 297, 385, 490, 627, 792, 1002, 1255, 1575, 1958, 2436, 3010, 3718, 4565, 5604, 6842, 8349, 10143, 12310, 14883, 17977, 21637, 26015, 31185, 37338, 44583, 53174, 63261, 75175, 89134]]]


To return no more than 3 results (default is 30), type

sage: len(sloane_find([1,2,3,4,5], 3))      # optional - internet
Searching Sloane's online database...
3


Sequence A137443 includes Sage code, and a “b file” that was computed with Sage:

sage: sloane_find([7, 71, 281, 4523, 74713])  # optional - internet
Searching Sloane's online database...
[[137443, 'First n-digit prime in consecutive digits of e.', [7, 71, 281, 4523, 74713, 904523, 6028747, 72407663, 360287471, 7427466391, 75724709369, 749669676277, 8284590452353, 99959574966967, 724709369995957, 2470936999595749, 28459045235360287, 571382178525166427]]]


Note that the OEIS (http://oeis.org/classic/) claims to limit the number of results to 100. Results are lists of the form [[number, description, list]], and invalid input will cause sloane_find to return [].

In some cases, these functions may return [] even though the inputs are legal. These cases correspond to errors from the OEIS server, and calling the functions again may fix the problem.

Alternatively, the SloaneEncyclopedia object provides access to a local copy of the database containing only the sequences and their names. To use this you must download and install the database using SloaneEncyclopedia.install(), or SloaneEncyclopedia.install_from_gz() if you have already downloaded the database manually.

To look up a sequence, type

sage: SloaneEncyclopedia[60843]               # optional - sloane_database
[1, 6, 21, 107]


To get the name of a sequence, type

sage: SloaneEncyclopedia.sequence_name(1)     # optional - sloane_database
'Number of groups of order n.'


To search locally for a particular subsequence, type

sage: SloaneEncyclopedia.find([1,2,3,4,5], 1)    # optional - sloane_database
[(15, [1, 2, 3, 4, 5, 7, 7, 8, 9, 11, 11, 13, 13, 16, 16, 16, 17, 19, 19, 23, 23, 23, 23, 25, 25, 27, 27, 29, 29, 31, 31, 32, 37, 37, 37, 37, 37, 41, 41, 41, 41, 43, 43, 47, 47, 47, 47, 49, 49, 53, 53, 53, 53, 59, 59, 59, 59, 59, 59, 61, 61, 64, 64, 64, 67, 67, 67, 71, 71, 71, 71, 73])]


The default maximum number of results is 30, but to return up to 100, type

sage: SloaneEncyclopedia.find([1,2,3,4,5], 100)    # optional - sloane_database
[(15, [1, 2, 3, 4, 5, 7, 7, 8, 9, 11, 11, ...


Results in either case are of the form [ (number, list) ].

TODO:

• When this program gets a sloane sequence from the database it actually downloads a huge amount of information about it, then throws most of it away. Also, it returns the data to the user as a very simple tuple. It would be much better to return an instance of a class:

class SloaneSequence: ...


and the class should have methods for each of the things that Sloane records about a sequence. Also, when possible, it should be able to compute more terms.

AUTHORS:

• Steven Sivek (2005-12-22): first version
• Steven Sivek (2006-02-07): updated to correctly handle the new search form on the Sloane website, and it’s now also smarter about loading the local database in that it doesn’t convert a sequence from string form to a list of integers until absolutely necessary. This seems to cut the loading time roughly in half.
• Steven Sivek (2009-12-22): added the SloaneEncyclopedia functions install() and install_from_gz() so users can get the latest versions of the OEIS without having to get an updated spkg; added sequence_name() to return the description of a sequence; and changed the data type for elements of each sequence from int to Integer.
class sage.databases.sloane.SloaneEncyclopediaClass

A local copy of the Sloane Online Encyclopedia of Integer Sequences that contains only the sequence numbers and the sequences themselves.

find(seq, maxresults=30)

Return a list of all sequences which have seq as a subsequence, up to maxresults results. Sequences are returned in the form (number, list).

INPUT:

• seq - list
• maxresults - int

OUTPUT: list of 2-tuples (i, v), where v is a sequence with seq as a subsequence.

install(oeis_url='http://oeis.org/classic/stripped.gz', names_url='http://oeis.org/classic/names.gz', overwrite=False)

Download and install the online encyclopedia, raising an IOError if either step fails.

INPUT:

• oeis_url - string (default: “http://www.research.att.com...”) The URL of the stripped.gz encyclopedia file.
• names_url - string (default: “http://www.research.att.com...”) The URL of the names.gz encyclopedia file. If you do not want to download this file, set names_url=None.
install_from_gz(stripped_file, names_file, overwrite=False)

Install the online encyclopedia from a local stripped.gz file.

INPUT:

• stripped_file - string. The name of the stripped.gz OEIS file.
• names_file - string. The name of the names.gz OEIS file, or None if the user does not want it installed.
• overwrite - boolean (default: False) If the encyclopedia is already installed and overwrite=True, install ‘filename’ over the old encyclopedia.

Load the entire encyclopedia into memory from a file. This is done automatically if the user tries to perform a lookup or a search.

sequence_name(N)

Return the name of sequence N in the encyclopedia. If sequence N does not exist, return ‘’. If the names database is not installed, raise an IOError.

INPUT:

• N - int

OUTPUT: string

EXAMPLES:

sage: SloaneEncyclopedia.sequence_name(1) # optional - sloane_database ‘Number of groups of order n.’

Remove the database from memory.

sage.databases.sloane.copy_gz_file(gz_source, bz_destination)

Decompress a gzipped file and install the bzipped verson. This is used by SloaneEncyclopedia.install_from_gz to install several gzipped OEIS database files.

INPUT:

• gz_source - string. The name of the gzipped file.
• bz_destination - string. The name of the newly compressed file.
sage.databases.sloane.parse_sequence(text)

x.__init__(...) initializes x; see help(type(x)) for signature

sage.databases.sloane.sloane_find(list, nresults=30, verbose=True)

Searches Sloane’s Online Encyclopedia of Integer Sequences for a sequence containing the number provided in list.

INPUT:

• list - (list) a list of integers to search Sloane’s for
• nresults - (integer) the maximum number of results to return default: 30
• verbose - (boolean) print a string to let the user know that it is working and not hanging. default: True

OUTPUT: A list of matches in Sloane’s database. Each match consists of a list of the sequence number, the name of the sequence, and some initial terms of the sequence.

EXAMPLES:

sage: sloane_find([1,1,2,3,5,8,13,21], nresults=1) #optional - internet
Searching Sloane's online database...
[[45,
'Fibonacci numbers: F(n) = F(n-1) + F(n-2), F(0) = 0, F(1) = 1, F(2) = 1, ...',
[0,
1,
1,
2,
3,
5,
8,
13,
21,
...
39088169]]]

sage.databases.sloane.sloane_sequence(number, verbose=True)

Returns a list with the number, name, and values for the sequence number in Sloane’s online database of integer sequences.

INPUT:

• number (integer) corresponding to the sequence.

• verbose - (boolean) print a string to let the user know that it is working and not hanging.

Set to True by default.

EXAMPLES:

sage: sloane_sequence(22) # optional - internet
Searching Sloane's online database...
[22,
'Number of centered hydrocarbons with n atoms.',
[0,
1,
0,
1,
...
36201693122]]


The input must not be a sequence itself:

sage: sloane_sequence(prime_range(100))
Traceback (most recent call last):
...
TypeError: input must be an integer or string that specifies the id of the Sloane sequence to download


Linear codes

#### Next topic

Frank Luebeck’s tables of Conway polynomials over finite fields