A124274 Nonprime numbers k that divide A124271(k) = Sum_{i=1..k} (prime(i)^k - 1) / (prime(i) - 1).

1, 9, 15, 121

Offset: 1

Author

Alexander Adamchuk, Oct 23 2006

Keywords

• bref
• hard
• more
• nonn

Comments

The next term if it exists is greater than 1000.

Note that a(1) = 1, a(2) = 3^2 and a(4) = 11^2 are perfect squares.

a(5) > 10^4, if it exists. - Amiram Eldar, Jul 25 2025

Examples

			9 is a term because 9 divides A124271(9) = 108336139407.
		

Crossrefs

Cf. A124271, A124273 (primes p that divide A124271(p)).

Programs

Mathematica

s={};Do[If[!PrimeQ[k],If[Divisible[Sum[(Prime[i]^k-1)/(Prime[i]-1),{i,k}],k],AppendTo[s,k]]],{k,10^3}];s (* James C. McMahon, Dec 10 2024 *)