A264526 Smallest number m such that both 2*n-m and 2*n+m are primes.

1, 1, 3, 3, 1, 3, 3, 1, 3, 9, 5, 3, 9, 1, 9, 3, 5, 9, 3, 1, 3, 15, 5, 3, 9, 7, 3, 15, 1, 9, 3, 5, 15, 3, 1, 15, 3, 5, 9, 15, 5, 3, 9, 7, 9, 15, 7, 9, 3, 1, 3, 3, 1, 3, 15, 13, 15, 9, 7, 9, 15, 13, 21, 21, 5, 3, 27, 1, 9, 15, 5, 33, 9, 1, 15, 3, 7, 9, 3, 5

Offset: 2

Author

Reinhard Zumkeller, Nov 17 2015

Keywords

• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 2..10000

Crossrefs

Cf. A014574, A040040, A082467, A088763, A260689, A264527.

Programs

Haskell

a264526 = head . a260689_row

Mathematica

snm[n_]:=Module[{m=1},While[!PrimeQ[2n-m]||!PrimeQ[2n+m],m=m+2];m]; Array[ snm,90,2] (* Harvey P. Dale, Aug 13 2017, optimized by Ivan N. Ianakiev, Mar 16 2018 *)

PARI

a(n) = {my(m=1); while(!(isprime(2*n-m) && isprime(2*n+m)), m+=2); m;} \\ Michel Marcus, Mar 18 2018

Formula

a(n) = A260689(n,1);

a(A040040(n)) = 1;

a(A014574(n)/2) = 1;

a(A088763(n)) = 3.

a(n) = A082467(2n). - Ivan N. Ianakiev, Oct 27 2021