A368201 Least k such that 9*n*k+1 is a prime.

2, 1, 4, 1, 4, 2, 2, 1, 2, 2, 2, 1, 8, 1, 2, 3, 2, 1, 12, 1, 2, 1, 4, 2, 8, 4, 2, 3, 2, 1, 4, 2, 6, 1, 2, 4, 6, 6, 10, 5, 2, 1, 4, 1, 2, 2, 4, 1, 2, 4, 2, 2, 14, 1, 2, 2, 4, 1, 2, 1, 14, 2, 4, 1, 2, 3, 12, 1, 6, 1, 2, 2, 6, 3, 6, 3, 6, 5, 2, 3, 2, 1, 6, 1, 2

Offset: 1

Author

Robert Price, Dec 16 2023

Keywords

• nonn

Links

• Robert Price, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A016014, A024906.

A070853 lists the corresponding primes.

Programs

Mathematica

A368201 = {};
Do[k=1; While[!PrimeQ[9 n k+1], k++]; AppendTo[A368201,k], {n,85}];
A368201

PARI

a(n) = my(k=1); while (!isprime(9*n*k+1), k++); k; \\ Michel Marcus, Dec 16 2023