A255429 Numbers with a prime number of nontrivial divisors.

6, 8, 10, 14, 15, 16, 21, 22, 26, 27, 33, 34, 35, 36, 38, 39, 46, 51, 55, 57, 58, 62, 64, 65, 69, 74, 77, 81, 82, 85, 86, 87, 91, 93, 94, 95, 100, 106, 111, 115, 118, 119, 122, 123, 125, 129, 133, 134, 141, 142, 143, 144, 145, 146, 155, 158, 159, 161, 166, 177, 178, 183, 185, 187, 194, 196

Offset

1,1

Comments

Empirically, numbers in this sequence seem to have few divisors.

This sequence appears to be the union of A130763 and the squares of A225649. - Kellen Myers, Apr 21 2015

Links

Table of n, a(n) for n=1..66.

Formula

{n: A070824(n) in A000040}.

Mathematica

seq[n_] := Select[Range[n], PrimeQ[DivisorSigma[0, #] - 2] &] (* Kellen Myers, Apr 21 2015 *)

Prog

(Magma) [n: n in [1..200] | IsPrime(NumberOfDivisors(n)-2)]; // Vincenzo Librandi, Apr 21 2015
(PARI) isok(m) = isprime(numdiv(m)-1); \\ Michel Marcus, Jan 13 2023

Crossrefs

Cf. A063806, A070824, A130763, A225649.

Sequence in context: A153032 A086822 A048943 * A319238 A331231 A130763

Adjacent sequences: A255426 A255427 A255428 * A255430 A255431 A255432

Keyword

nonn

Author

Rory Glover, Feb 22 2015

Extensions

Terms fixed by Kellen Myers, Apr 21 2015

Name corrected by Michel Marcus, Jan 13 2023

Status

approved