OFFSET
1,2
COMMENTS
It is an open problem to find all numbers k such that (k+1)*(k-1) is a divisor of 3^k + 5^k.
In particular, it is not known if the intersection of this sequence and A234535 equals {3}. - Max Alekseyev, May 19 2015
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..600
Daniel Kohen et al., On Polynomials dividing Exponentials, MathOverflow.
Byron Schmuland et al., Find all positive integers n such that 3^n + 5^n is divisible by n^2 - 1, Math StackExchange.
MATHEMATICA
Select[Range[10^6], Mod[PowerMod[3, #, # + 1] + PowerMod[5, #, # + 1], # + 1] == 0 &]
PROG
(PARI) isok(k) = Mod(3, k+1)^k + Mod(5, k+1)^k == 0; \\ Michel Marcus, Aug 04 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Siad Daboul, Dec 27 2013
EXTENSIONS
a(1) inserted by Amiram Eldar, Jul 31 2021
STATUS
approved