|
%I #27 May 12 2015 10:54:35
%S 1,2,4,8,16,23,32,37,46,47,53,64,67,74,79,83,89,92,94,97,106,113,127,
%T 128,131,134,148,157,158,163,166,167,173,178,184,188,194,211,212,223,
%U 226,233,251,254,256,257,262,263,268,277,293,296
%N n not divisible by any prime=p, where either p-2 or p+2 is prime.
%C Complement of A062506.
%C n divisible only by single primes A007510. - Zak Seidov, May 11 2015
%H Robert Israel, <a href="/A062729/b062729.txt">Table of n, a(n) for n = 1..10000</a>
%e 46 is included because 46 = 2 * 23 and all (2+2), (2-2), (23+2), (23-2) are composite. (* edited by _Zak Seidov_, May 11 2015 *)
%p N:= 1000: # to get all terms <= N
%p Primes:= select(isprime, {2,(2*i+1)$i=1..ceil((N+1)/2)}):
%p LTwins:= Primes intersect map(`-`,Primes,2):
%p A:= Vector(N):
%p for p in LTwins do
%p A[p*[$1..floor(N/p)]]:= 1;
%p A[(p+2)*[$1..floor(N/(p+2))]]:= 1;
%p od:
%p select(t -> A[t]<>1, [$1..N]); # _Robert Israel_, May 11 2015
%t Select[Range@296, #==1 || (p = First /@ FactorInteger@#; Nor @@ Flatten@ PrimeQ@ {p+2, p-2}) &] (* _Giovanni Resta_, May 12 2015 *)
%o (PARI) isok(n) = {my(f = factor(n)); for (i=1, #f~, p = f[i, 1]; if (isprime(p-2) || isprime(p+2), return (0));); return (1);} \\ _Michel Marcus_, May 20 2014
%Y Cf. A062506, A007510. - _Zak Seidov_, May 11 2015
%K nonn
%O 1,2
%A _Leroy Quet_, Jul 11 2001
%E Offset changed to 1 by _Michel Marcus_, May 20 2014
|
