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A191236 Number of ways to place n nonattacking bishops on black squares of a 2n X 2n board. 5
1, 2, 14, 184, 3532, 89256, 2800016, 104967808, 4578528464, 227816059360, 12735645181536, 790296855912576, 53905019035510528, 4008716449677965312, 322807879692969879552, 27983800239966141382656 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..340

V. Kotesovec, Number of ways of placing non-attacking queens, kings, bishops and knights (in English and Czech)

FORMULA

a(n) = 1/n! * Sum_{j=0..n} (-1)^(n-j) * binomial(n,j) * (j*(j+1))^n.

Asymptotic: a(n) ~ 1/sqrt(Pi*(z-1)*(2-z)*n)*(2*n*exp(z-1)/z)^n or a(n) ~ exp(z/2)*StirlingS2(2*n,n) where z = A256500 = 1.59362426... is a root of the equation exp(z)*(2-z)=2.

O.g.f.: Sum_{n>=0} n^n*(n+1)^n * exp(-n*(n+1)*x) * x^n/n! = Sum_{n>=0} a(n)*x^n. - Paul D. Hanna, Oct 15 2012

a(n) = Sum_{k=0..n} binomial(n,k) * Stirling2(2*n-k,n), where Stirling2(n,k) = A008277(n,k). - Paul D. Hanna, Nov 13 2012

MATHEMATICA

Join[{1}, Table[(1/n!)*Sum[(-1)^(n - k)*Binomial[n, k]*(k*(k + 1))^n, {k, 0, n}], {n, 1, 50}]] (* G. C. Greubel, Feb 03 2017 *)

PROG

(PARI) {a(n)=polcoeff(sum(m=0, n, m^m*(m+1)^m*x^m*exp(-m*(m+1)*x+x*O(x^n))/m!), n)} \\ Paul D. Hanna, Oct 15 2012

(PARI) {Stirling2(n, k)=n!*polcoeff(((exp(x+x*O(x^n))-1)^k)/k!, n)}

{a(n)=sum(k=0, n, binomial(n, k) * Stirling2(2*n-k, n))} \\ Paul D. Hanna, Nov 13 2012

CROSSREFS

Cf. A002465, A187235, A217905.

Sequence in context: A258872 A000807 A191565 * A217905 A237852 A219874

Adjacent sequences:  A191233 A191234 A191235 * A191237 A191238 A191239

KEYWORD

nonn

AUTHOR

Vaclav Kotesovec, May 27 2011

EXTENSIONS

Offset changed to 0 and a(0)=1 added by Paul D. Hanna, Nov 13 2012

STATUS

approved

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Last modified July 19 09:33 EDT 2019. Contains 325155 sequences. (Running on oeis4.)