A074592 - OEIS

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A074592

Smallest prime factors of numbers that are not prime powers.

2, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 2, 2, 3, 2, 5, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 5, 2, 3, 2, 2, 2, 3, 5, 2, 2, 3, 2, 2, 2, 3, 2, 7, 2, 2, 2, 2, 5, 2, 3, 2, 2, 7, 2, 3, 2, 5, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 5, 2, 3, 2, 7, 2, 2, 3, 2, 2, 3, 2, 2, 7, 2, 3, 2, 2, 2, 3, 2, 11, 2, 5, 2, 3, 2, 2, 2, 3, 2

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A020639(A024619(n)).

a(n) > 2 iff n+1 and n+2 are prime powers (A006549).

MATHEMATICA

s[n_] := Module[{f = FactorInteger[n]}, If[Length[f] > 1, f[[1, 1]], Nothing]]; Array[s, 200] (* Amiram Eldar, Oct 10 2024 *)

CROSSREFS

Cf. A006549, A020639, A024619, A074593, A074594, A074595.