A036981 Number of (2n+1) X (2n+1) symmetric matrices each of whose rows is a permutation of 1..(2n+1).

1, 6, 720, 31449600, 444733651353600, 10070314878246926155776000, 614972203951464612786852376432607232000

Offset: 0

Author

Joshua Zucker and Joe Keane

Keywords

• nonn
• more

Comments

Number of different schedules for 2n+2 teams. - Andres Cardemil (andrescarde(AT)yahoo.com), Nov 28 2001

Links

• Minjia Shi, Li Xu, and Denis S. Krotov, The number of the non-full-rank Steiner triple systems, arXiv:1806.00009 [math.CO], 2018-2021.
• Index entries for sequences related to tournaments.

Crossrefs

Cf. A000438, A000474, A035481, A036980, A064120, A065594.

Formula

a(n) = A000438(n+1) * (2*n+1)!.

Extensions

a(5)-a(6) computed from A000438 by Max Alekseyev, Jun 17 2011