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

1,1

Comments

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

Links

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

Formula

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

Mathematica

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

Prog

(PARI) vector(100, n, vecmin(factor(6*n+1)[, 1])) \\ Altug Alkan, Oct 23 2015
(Magma) [Min(PrimeFactors(6*n+1)):n in[1..68]]; // Jason Kimberley, Oct 28 2015

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)).

Sequence in context: A212454 A266731 A104995 * A254762 A275681 A173928

Adjacent sequences: A107741 A107742 A107743 * A107745 A107746 A107747

Keyword

nonn

Author

Zak Seidov, May 23 2005

Extensions

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

Status

approved