A391157 Triangle read by rows: T(n,k) is the number of labeled semigroups with n elements whose center contains k elements.

1, 0, 1, 2, 0, 6, 26, 24, 0, 63, 944, 664, 744, 0, 1140, 53242, 35780, 32480, 31500, 0, 30730, 4645942, 2823984, 3482160, 3014160, 1909800, 0, 1185072, 605080534, 317296420, 1313004924, 4470358200, 764186360, 206766420, 0, 66363206

Offset

0,4

Links

Table of n, a(n) for n=0..35.

Wikipedia, Center (algebra).

Index entries for sequences related to semigroups.

Example

Triangle begins:
        1;
        0,       1;
        2,       0,       6;
       26,      24,       0,      63;
      944,     664,     744,       0,    1140;
    53242,   35780,   32480,   31500,       0, 30730;
  4645942, 2823984, 3482160, 3014160, 1909800,     0, 1185072;
  ...

Crossrefs

Row sums are A023814.

Main diagonal is A023815.

Column k=0 is A391158.

Cf. A058166, A391154, A391159 (unlabeled version).

Sequence in context: A362685 A171734 A278746 * A280217 A079203 A151751

Adjacent sequences: A391154 A391155 A391156 * A391158 A391159 A391160

Keyword

nonn,tabl,more

Author

Andrew Howroyd, Dec 10 2025

Status

approved