A316330 a(n) = A000085(4*n)/2^n.

1, 5, 191, 17519, 2887921, 742458253, 273315477775, 136025604432743, 87816638377854497, 71278145791452802133, 70978809757898186241439, 85023410230409691052228255, 120545000629512292505954394769, 199558149588334620585072909701981, 381323441275017330119775857868585839

Offset: 0

Author

N. J. A. Sloane, Jul 09 2018, following a suggestion from Doron Zeilberger

Keywords

• nonn

Links

• Seiichi Manyama, Table of n, a(n) for n = 0..210
• S. Chowla, I. N. Herstein and W. K. Moore, On recursions connected with symmetric groups I, Canad. J. Math. 3 (1951) 328-334.
• Dongsu Kim and Jang Soo Kim, A combinatorial approach to the power of 2 in the number of involutions, J. Comb. Theory Ser. A 117 (8) (2010): 1082-1094.

Crossrefs

Cf. A000085, A316331, A316332, A316333.