%I #24 Feb 01 2024 01:47:47

%S 3,6,9,12,14,18,24,27,28,30,36,38,42,48,54,56,60,62,72,74,76,81,84,90,

%T 96,98,102,108,110,112,114,120,124,126,138,144,148,150,152,158,162,

%U 168,174,180,182,192,194,196,204,216,220,224,228,230,240,243,248,252

%N Numbers k such that rad(k) - 1 is prime.

%H Amiram Eldar, <a href="/A359213/b359213.txt">Table of n, a(n) for n = 1..10000</a>

%e rad(60) - 1 = 2*3*5 - 1 = 29, so 60 is a term.

%t Select[Range[250], PrimeQ[Times @@ FactorInteger[#][[;; , 1]] - 1] &] (* _Amiram Eldar_, Dec 21 2022 *)

%o (PARI) isok(k) = isprime(factorback(factor(k)[, 1]) - 1); \\ _Michel Marcus_, Dec 22 2022

%Y Cf. A007947, A097379.

%K nonn

%O 1,1

%A _Arsen Vardanyan_, Dec 21 2022