A064271 Numbers k such that sigma(k) - 2k is prime.

18, 20, 36, 100, 104, 196, 324, 392, 464, 576, 650, 784, 800, 900, 968, 1352, 1936, 1952, 2450, 2500, 3136, 4356, 4624, 5184, 6050, 6400, 9216, 10000, 10404, 10816, 12800, 13456, 14400, 15376, 15488, 16928, 18496, 20000, 20736, 23104, 26912

Offset

1,1

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Example

n=100: sigma(100) - 2*100 = 17, a prime.

Prog

(PARI) j=[]; for(n=1, 50000, x=sigma(n)-2*n; if(x>0 && isprime(x), j=concat(j, n))); j
(PARI) { n=0; for (m=1, 10^9, if (isprime(sigma(m) - 2*m), write("b064271.txt", n++, " ", m); if (n==1000, break)) ) } \\ Harry J. Smith, Sep 11 2009

Crossrefs

Cf. A000203, A033880.

Sequence in context: A350038 A335897 A036170 * A113541 A181453 A113542

Adjacent sequences: A064268 A064269 A064270 * A064272 A064273 A064274

Keyword

easy,nonn

Author

Jason Earls, Sep 23 2001

Status

approved