OFFSET
1,3
COMMENTS
E. Vantieghem proved that a(n) = n if and only if n is an odd prime (see link).
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
E. Vantieghem, On a congruence only holding for primes, Indagationes Mathematicae, Volume 2, Issue 2, 17 June 1991, pp. 253-255.
MAPLE
a:= proc(n) local d, m, r; r, m:= 1, 2^n-1;
for d to n-1 do r:= irem(r*(2^d-1), m) od;
irem(r, m)
end:
seq(a(n), n=0..40); # Alois P. Heinz, Apr 17 2013
MATHEMATICA
Table[Mod[Product[2^d-1, {d, 1, n-1}], 2^n-1], {n, 1, 37}] (* Geoffrey Critzer, Sep 28 2013 *)
PROG
(PARI) a(n) = prod(d=1, n-1, 2^d-1) % (2^n-1) \\ Michel Marcus, Apr 17 2013
CROSSREFS
Cf. A219732.
KEYWORD
nonn
AUTHOR
Michel Marcus, Apr 17 2013
STATUS
approved