OFFSET
1,3
COMMENTS
if a(n) > 0 then 2n-1, except n=5 and n=13, is prime.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
f:= proc(n)
local m, r, p, k;
m:= floor(2*n/3);
r:= 2*n-1;
p:= 1;
for k from 1 to m do
p:= p*k mod r;
if p = 0 then break fi;
od:
p
end proc:
f(1):= 0:
map(f, [$1..100]); # Robert Israel, Mar 08 2017
MATHEMATICA
Table[Mod[Floor[(2n)/3]!, 2n-1], {n, 80}] (* Harvey P. Dale, Aug 21 2024 *)
PROG
(PARI) a(n) = (2*n\3)! % (2*n-1); \\ Michel Marcus, Mar 07 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Zhandos Mambetaliyev, Mar 06 2017
EXTENSIONS
More terms from Michel Marcus, Mar 07 2017
STATUS
approved