OFFSET
1,2
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
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 *)
MAPLE
N:= 1000: # to get all terms <= N
Primes:= select(isprime, {2, (2*i+1)$i=1..ceil((N+1)/2)}):
LTwins:= Primes intersect map(`-`, Primes, 2):
A:= Vector(N):
for p in LTwins do
A[p*[$1..floor(N/p)]]:= 1;
A[(p+2)*[$1..floor(N/(p+2))]]:= 1;
od:
select(t -> A[t]<>1, [$1..N]); # Robert Israel, May 11 2015
MATHEMATICA
Select[Range@296, #==1 || (p = First /@ FactorInteger@#; Nor @@ Flatten@ PrimeQ@ {p+2, p-2}) &] (* Giovanni Resta, May 12 2015 *)
PROG
(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
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Jul 11 2001
EXTENSIONS
Offset changed to 1 by Michel Marcus, May 20 2014
STATUS
approved