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A182562
Number of ways to place k non-attacking semi-knights on an n x n chessboard, sum over all k>=0
2
2, 16, 288, 11664, 1458000, 506250000, 414720000000, 869730877440000, 5045702916833280000, 77297454895962562560000, 3017525202366485003182080000, 307389127582207654481154908160000, 83016370640108703579427655610531840000, 58770343311359208383258439665073059266560000
OFFSET
1,1
COMMENTS
Semi-knight is a semi-leaper [1,2]. Moves of a semi-knight are allowed only in [2,1] and [-2,-1]. See also semi-bishops (A187235).
LINKS
FORMULA
a(n) = F(n/2+2)^(n+2)*prod(j=1,n/2-1,F(j+2)^4) if n is even, F((n+1)/2+2)^((n+1)/2)*F((n-1)/2+2)^((n-1)/2)*prod(j=1,(n-1)/2,F(j+2)^4) if n is odd, where F(n) = A000045(n) is the n-th Fibonacci number.
a(n) is asymptotic to C^4*((1+sqrt(5))/2)^((n+2)*(n+4))/5^(3/2*(n+2)), where C=1.226742010720353244... is Fibonacci Factorial Constant, see A062073.
MATHEMATICA
Table[If[EvenQ[n], Fibonacci[n/2+2]^(n+2)*Product[Fibonacci[j+2]^4, {j, 1, n/2-1}], Fibonacci[(n+1)/2+2]^((n+1)/2)*Fibonacci[(n-1)/2+2]^((n-1)/2)*Product[Fibonacci[j+2]^4, {j, 1, (n-1)/2}]], {n, 1, 20}]
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, May 05 2012
STATUS
approved