A188539 Numbers n such that n^2 plus number of divisors of n^2 is prime.

1, 2, 8, 10, 36, 38, 40, 44, 52, 58, 62, 68, 76, 80, 82, 98, 104, 108, 118, 124, 130, 136, 142, 154, 160, 170, 172, 182, 202, 208, 212, 218, 236, 238, 242, 266, 284, 290, 298, 316, 338, 356, 358, 364, 376, 382, 388, 410

Offset

1,2

Comments

All terms > 1 are even. - Robert Israel, Apr 11 2018

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

select(n -> isprime(n^2 + numtheory:-tau(n^2)), [1, seq(i, i=2..1000, 2)]); # Robert Israel, Apr 11 2018

Mathematica

Select[Range[500], PrimeQ[#^2 + DivisorSigma[0, #^2]] &] (* Alonso del Arte, Apr 08 2011 *)

Prog

(PARI) is(n)=isprime(numdiv(n^2)+n^2) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A188665, A000005.

Sequence in context: A062880 A066707 A107227 * A230826 A071184 A174153

Adjacent sequences: A188536 A188537 A188538 * A188540 A188541 A188542

Keyword

nonn

Author

Juri-Stepan Gerasimov, Apr 07 2011

Status

approved