A320517 Prime k with sigma(sigma(sigma(k))) < 3*k + 1.

3, 97, 241, 337, 577, 1249, 3361, 3697, 4801, 6961, 8191, 10657, 14449, 16561, 18049, 23761, 25537, 31249, 32257, 37537, 48049, 49297, 64081, 65521, 77617, 79201, 89041, 120049, 126001, 138337, 140449, 153457, 171697, 174049, 181201, 193441, 208657, 216481

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..1000

Maple

with(numtheory, sigma):
isA320517 := n -> isprime(n) and (sigma(sigma(sigma(n))) < 3*n + 1):
S := select(isA320517, [$1..300000]);

Mathematica

Select[Range[250000], PrimeQ[#] && DivisorSigma[1, DivisorSigma[1, DivisorSigma[1, #]]] < 3*# + 1 &] (* Vaclav Kotesovec, Oct 14 2018 *)

Prog

(PARI) isok(n) = isprime(n) && (sigma(sigma(sigma(n))) < 3*n + 1); \\ Michel Marcus, Oct 14 2018

Crossrefs

Cf. A000203, A320513.

Sequence in context: A100494 A209554 A320513 * A348491 A243155 A201843

Adjacent sequences: A320514 A320515 A320516 * A320518 A320519 A320520

Keyword

nonn

Author

Peter Luschny, Oct 14 2018

Status

approved