OFFSET
4,2
LINKS
Indranil Ghosh, Table of n, a(n) for n = 4..80
FORMULA
a(n) = binomial(n,4)*2^(binomial(n,2)-6).
The number of size p cliques in all simple labeled graphs is binomial(n,p)*2^(binomial(n,2)-binomial(p,2)).
E.g.f.: x^4/4!*A(16x) where A(x) is the e.g.f. for A006125. - Geoffrey Critzer, Apr 13 2017
EXAMPLE
a(6) = binomial(6,4)*2^(binomial(6,2)-6) = 15 * 2^(15-6) = 15 * (2^9) = 7680. - Indranil Ghosh, Feb 25 2017
MATHEMATICA
Table[Binomial[n, 4] 2^(Binomial[n, 2] - 6), {n, 4, 15}]
PROG
(PARI) a(n) = binomial(n, 4)*2^(binomial(n, 2)-6) \\ Indranil Ghosh, Feb 25 2017
(Python)
import math
f=math.factorial
def C(n, r): return f(n)/f(r)/f(n-r)
def A278736(n): return C(n, 4)*2**(C(n, 2)-6) # Indranil Ghosh, Feb 25 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Geoffrey Critzer, Nov 27 2016
STATUS
approved