A294431 Rank of the inverse semigroup D_n of all difunctional relations on an n-element set.

1, 2, 3, 8, 19, 57, 209, 884, 4148, 21156, 115985, 678581, 4213609, 27644450, 190899336, 1382958560, 10480142163, 82864869821, 682076806177, 5832742205076, 51724158235392, 474869816156772, 4506715738447345, 44152005855084369, 445958869294805313, 4638590332229999378

Offset

0,2

Links

Table of n, a(n) for n=0..25.

James East, A. Vernitski, Ranks of ideals in inverse semigroups of difunctional binary relations, arXiv preprint arXiv:1612.04935 [math.GR], 2016.

Formula

a(n) = A000110(n) + n for n >= 3 (see Theorem 2.3 of the East-Vernistki paper). - James East, Feb 27 2018

Crossrefs

The rightmost diagonal of A294432.

Sequence in context: A148041 A148042 A077269 * A148043 A321255 A243791

Adjacent sequences: A294428 A294429 A294430 * A294432 A294433 A294434

Keyword

nonn

Author

N. J. A. Sloane, Nov 13 2017

Extensions

More terms from James East, Feb 27 2018

Status

approved