OFFSET
1,3
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..1000
P. Erdos, R. L. Graham, I. Z. Russa and E. G. Straus, On the prime factors of C(2n,n), Math. Comp. 29 (1975), 83-92.
Peter Luschny, On the prime factors of the swinging factorial.
MAPLE
MATHEMATICA
(* A naive solution *) sf[n_] := n!/Quotient[n, 2]!^2; Select[Range[0, 16000], !Divisible[sf[#], 3] && !Divisible[sf[#], 5] &] (* Jean-François Alcover, Jun 28 2013 *)
PROG
(PARI) valp(n, p)=my(s); while(n\=p, s+=n); s
is(n)=valp(n, 3)==2*valp(n\2, 3) && valp(n, 5)==2*valp(n\2, 5) \\ Charles R Greathouse IV, Feb 02 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Oct 06 2011
STATUS
approved