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A322299 Number of distinct automorphism group sizes for binary self-dual codes of length 2n. 5
1, 1, 1, 2, 2, 3, 4, 7, 9, 16, 24, 48, 85, 149, 245, 388 (list; graph; refs; listen; history; text; internal format)
Codes are vector spaces with a metric defined on them. Specifically, the metric is the hamming distance between two vectors. Vectors of a code are called codewords.
A code is usually represented by a generating matrix. The row space of the generating matrix is the code itself.
Self-dual codes are codes such all codewords are pairwise orthogonal to each other.
Two codes are called permutation equivalent if one code can be obtained by permuting the coordinates (columns) of the other code.
The automorphism group of a code is the set of permutations of the coordinates (columns) that result in the same identical code.
W. Cary Huffman and Vera Pless, Fundamentals of Error Correcting Codes, 2003, pp. 7, 252-330, 338-393.
There are a(16) = 388 distinct sizes for the automorphism groups of the binary self-dual codes of length 16. In general, two automorphism groups with the same size are not necessarily isomorphic.
Cf. self-dual codes A028362, A003179, A106162, A028363, A106163.
Sequence in context: A277252 A241415 A323357 * A003179 A153934 A361440
Nathan J. Russell, Dec 02 2018

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