OFFSET
1,3
COMMENTS
S(2,2,1) is the star graph with two legs of length two and one of length one.
LINKS
Index entries for linear recurrences with constant coefficients, signature (12,-60,160,-240,192,-64).
FORMULA
a(n) = (2^n)*(C(n,3))*(3n)*(n-2).
G.f.: 24*x^3*(3 + 28*x + 12*x^2)/(1 - 2*x)^6. - Stefano Spezia, Apr 15 2022
Sum_{n>=3} 1/a(n) = 13/32 + 3*log(2)^2/16 - log(2)/4 - Pi^2/32. - Amiram Eldar, Apr 22 2022
MATHEMATICA
a[n_] := (2^n)*Binomial[n, 3]*3*n*(n-2); Array[a, 24] (* Amiram Eldar, Apr 22 2022 *)
PROG
(Python) from math import comb
def a(n):
return (2**n)*comb(n, 3)*3*n*(n-2)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Ben Eck, Apr 14 2022
STATUS
approved