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Nonprimes excluding numbers of the forms 2*p and p^i where p is a prime and i is a positive integer.
4

%I #36 Dec 06 2015 08:02:40

%S 0,1,12,15,18,20,21,24,28,30,33,35,36,39,40,42,44,45,48,50,51,52,54,

%T 55,56,57,60,63,65,66,68,69,70,72,75,76,77,78,80,84,85,87,88,90,91,92,

%U 93,95,96,98,99,100,102,104,105,108,110,111,112,114,115,116

%N Nonprimes excluding numbers of the forms 2*p and p^i where p is a prime and i is a positive integer.

%t Select[Range@ 120, And[! PrimeQ@ #, Nand[EvenQ@ #, PrimeQ[#/2]], ! PrimePowerQ@ #] &] (* _Michael De Vlieger_, Dec 02 2015 *)

%o (PARI) isok(n) = ! (isprime(n) || (! (n%2) && isprime(n/2)) || isprimepower(n)); \\ _Michel Marcus_, Dec 02 2015

%Y Cf. A000961, A024619, A100484, A264828.

%K nonn,easy

%O 1,3

%A _Giovanni Teofilatto_, Dec 02 2015