A367970 Least k such that 5*n*k+1 is a prime.

2, 1, 2, 2, 4, 1, 2, 1, 4, 2, 6, 1, 2, 1, 2, 3, 12, 2, 2, 1, 2, 3, 4, 2, 2, 1, 2, 2, 10, 1, 2, 4, 2, 6, 4, 1, 8, 1, 6, 2, 4, 1, 2, 3, 8, 2, 4, 1, 2, 1, 4, 2, 4, 1, 12, 1, 2, 5, 4, 2, 6, 1, 2, 2, 4, 1, 6, 3, 2, 2, 6, 5, 18, 4, 2, 2, 6, 3, 6, 1, 2, 2, 28, 1, 6

Offset: 1

Author

Robert Price, Dec 17 2023

Keywords

• nonn

Links

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

Crossrefs

Cf. A016014, A024894.

A070849 lists the corresponding primes.

Programs

Mathematica

A367970 = {};
Do[k=1; While[!PrimeQ[5 n k+1], k++]; AppendTo[A367970 ,k], {n,85}];
A367970

PARI

a(n) = my(k=1); while (!isprime(5*n*k+1), k++); k; \\ Michel Marcus, Dec 17 2023