A236917 Numbers n for which there is no k such that n - k and n + k are both prime, with 0 <= k <= sqrt(n).

1, 8, 22, 24, 25, 28, 32, 35, 38, 46, 49, 51, 52, 55, 58, 62, 68, 74, 80, 82, 85, 87, 91, 94, 112, 114, 115, 116, 119, 121, 123, 124, 125, 126, 128, 130, 136, 142, 146, 152, 155, 164, 166, 175, 178, 184, 200, 203, 206, 207, 208, 209, 212, 214, 215, 216, 218

Offset: 1

Author

Juri-Stepan Gerasimov, Feb 01 2014

Keywords

• nonn

Comments

Numbers n such that A236747(n) = 0.

Probably finite. Perhaps a(4565) = 2591107 is the last term; any other terms are greater than 10^9. - Charles R Greathouse IV, Feb 03 2014

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..4565

Programs

Mathematica

nkQ[n_]:=!PrimeQ[n]&&Count[PrimeQ/@Table[n+{k,-k},{k,Floor[Sqrt[n]]}],?(# == {True,True}&)]==0; Select[Range[250],nkQ] (* _Harvey P. Dale, Jun 08 2022 *)

PARI

is(n)=for(k=0,sqrtint(n),if(isprime(n-k)&&isprime(n+k), return(0))); 1 \\ Charles R Greathouse IV, Feb 03 2014