A062514 Numbers k such that sigma(phi(k)) is a prime.

3, 4, 5, 6, 8, 10, 12, 17, 32, 34, 40, 48, 60, 85, 128, 136, 160, 170, 192, 204, 240, 4369, 8192, 8224, 8704, 8738, 10240, 10280, 10880, 12288, 12336, 13056, 15360, 15420, 16320, 65537, 131072, 131074, 131584, 139264, 139808, 163840, 164480, 174080

Offset: 1

Author

Jason Earls, Jul 09 2001

Keywords

• easy
• nonn

Comments

Numbers k such that A062402(k) is prime.

Examples

			Phi(174080)=65536. Sigma(65536) = 131071, a prime.
		

Links

• Michel Marcus, Table of n, a(n) for n = 1..105 (terms 1..73 from Harry J. Smith)

Crossrefs

Cf. A000010, A000203, A062402.

Programs

PARI

je=[]; for(n=1,300000,s=sigma(eulerphi(n)); if(isprime(s),je=concat(je,n))); je

PARI

{ n=0; for (m=1, 10^9, if(isprime(sigma(eulerphi(m))), write("b062514.txt", n++, " ", m); if (n==73, break)) ) } \\ Harry J. Smith, Aug 08 2009