A072064 Least k>0 such that prime(n)+k*n is prime.

1, 1, 2, 1, 4, 1, 2, 3, 2, 3, 2, 2, 2, 2, 4, 3, 4, 1, 6, 3, 4, 1, 10, 1, 4, 1, 2, 2, 2, 2, 4, 1, 4, 1, 6, 2, 6, 2, 6, 3, 24, 1, 2, 2, 6, 3, 8, 1, 6, 3, 8, 5, 2, 2, 2, 3, 2, 4, 6, 2, 16, 3, 2, 2, 2, 1, 4, 3, 6, 1, 10, 1, 4, 2, 6, 6, 16, 3, 8, 2, 4, 1, 6, 2, 10, 3, 4, 4, 18, 2, 6, 1, 2

Offset: 1

Author

Reinhard Zumkeller, Jun 12 2002

Keywords

• nonn

Examples

			n=3, prime(3)=5: 5+1*3=8 is not prime, but 5+2*3=11, therefore a(3)=2 and A072063(3)=11.
		

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A034693, A000040, A072063.

Programs

Mathematica

A072064[n_]:=Module[{p=Prime[n],k=1},While[!PrimeQ[p+k*n],k++];k];Array[A072064,100] (* Paolo Xausa, Nov 27 2023 *)

PARI

a(n) = my(p=prime(n), k=1); while (!isprime(p+k*n), k++); k; \\ Michel Marcus, Nov 27 2023