OFFSET
1,1
COMMENTS
a(n) = A002720(n) if n is odd.
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..440
V. Kotesovec, Non-attacking chess pieces
FORMULA
Recurrence: a(n) = ((12*n^5 - 158*n^4 - (6*(-1)^n-706)*n^3 - (1193-41*(-1)^n)*n^2 - 8*(7*(-1)^n-72)*n - 22*(-1)^n-28)*a(n-2) + (-12*n^6 + 206*n^5 + 2*(7*(-1)^n-691)*n^4 + (4545-137*(-1)^n)*n^3 + (442*(-1)^n-7442)*n^2 + (5194-544*(-1)^n)*n + 198*(-1)^n-698)*(n-2)*a(n-4) + 2*(2*n-1)*(n^2-7*n+10)^2*(n-4)^4*a(n-6))/(2*(n-5)^2*(2*n-5)).
MATHEMATICA
Table[Sum[If[EvenQ[n], 2^k*k!*Sum[Binomial[n/2, i]^2*Binomial[n/2, k-i]^2/Binomial[k, i], {i, 0, k}], Binomial[n, k]^2*k!], {k, 0, n}], {n, 1, 25}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Aug 28 2012
STATUS
approved