OFFSET
1,3
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..30
Mathoverflow, Probability of a graph procedure.
FORMULA
For n>1, a(n) = binomial(n,2)! * 2^(n-2) / A000108(n-1).
MATHEMATICA
Join[{1}, Table[Binomial[n, 2]!*2^(n-2)*n/Binomial[2*n-2, n-1], {n, 2, 20}]] (* G. C. Greubel, Aug 03 2018 *)
PROG
(PARI) {a(n) = if( n<2, n>0, binomial(n, 2)! * 2^(n-2) * n / binomial(2*n-2, n-1))}; /* Michael Somos, Jul 23 2015 */
(Magma) [1] cat [Factorial(Binomial(n, 2))*2^(n-2)*n/Binomial(2*n-2, n-1): n in [2..20]]; // G. C. Greubel, Aug 03 2018
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
Max Alekseyev, Mar 09 2015
STATUS
approved