A107744 Smallest prime factor of 6*n+1.

7, 13, 19, 5, 31, 37, 43, 7, 5, 61, 67, 73, 79, 5, 7, 97, 103, 109, 5, 11, 127, 7, 139, 5, 151, 157, 163, 13, 5, 181, 11, 193, 199, 5, 211, 7, 223, 229, 5, 241, 13, 11, 7, 5, 271, 277, 283, 17, 5, 7, 307, 313, 11, 5, 331, 337, 7, 349, 5, 19, 367, 373, 379, 5, 17, 397, 13, 409

Offset: 1

Author

Zak Seidov, May 23 2005

Keywords

• nonn

Comments

If 6*n+1 is prime, a(n) = 6*n+1.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A016921, A020639.

Cf. A107745 (smallest prime factor of 6*n-1), A107746 (values of k such that A107744(k) > A107745(k)), A107747 (values of k such that A107744(k) < A107745(k)).

Programs

Magma

[Min(PrimeFactors(6*n+1)):n in[1..68]]; // Jason Kimberley, Oct 28 2015

Mathematica

A107744[n_]:= FactorInteger[6 n + 1][[1, 1]]

PARI

vector(100, n, vecmin(factor(6*n+1)[, 1])) \\ Altug Alkan, Oct 23 2015

Formula

a(n) = A020639(A016921(n)). - Amiram Eldar, Nov 03 2024

Extensions

Comments corrected and (at the suggestion of Michel Marcus) moved to Crossrefs by Jason Kimberley, Oct 23 2015