OFFSET
0,2
LINKS
Jayanta Basu, Table of n, a(n) for n = 0..1000
EXAMPLE
5!! = 5*3*1 = 15; 5+4+3+2+1 = 15; 15/15 = 1.
13!! = 13*11*9*7*5*3*1 = 135135; 13+12+11+10+9+8+7+6+5+4+3+2+1 = 91; 135135/91 = 1485.
MAPLE
P:=proc(n) local a, i, j, k, w; for i from 1 by 1 to n do k:=i; w:=i-2; while w>0 do k:=k*w; w:=w-2; od; j:=sum('w', 'w'=1..i); a:=k/j; if trunc(a)=a then print(i) fi; od; end: P(100);
MATHEMATICA
pr[n_] := Times @@ If[OddQ[n], Range[1, n, 2], Range[2, n, 2]]; Select[Range[122], Divisible[pr[#], Total[Range[#]]] &] (* Jayanta Basu, Aug 11 2013 *)
Select[Range[200], Divisible[#!!, (#(#+1))/2]&] (* Harvey P. Dale, Feb 09 2015 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paolo P. Lava and Giorgio Balzarotti, May 24 2007
EXTENSIONS
More terms from Jayanta Basu, Aug 11 2013
STATUS
approved