A379640 Smallest primitive prime factor of 7^n-1.

2, 1, 19, 5, 2801, 43, 29, 1201, 37, 11, 1123, 13, 16148168401, 113, 31, 17, 14009, 117307, 419, 281, 11898664849, 23, 47, 73, 2551, 53, 109, 13564461457, 59, 6568801, 311, 353, 3631, 29078814248401, 2127431041, 13841169553, 223, 351121, 486643, 41, 83, 51031

Offset: 1

Author

Sean A. Irvine, Dec 28 2024

Keywords

• nonn

Comments

Also, smallest prime p such that 1/p has septimal period n.

Links

• Max Alekseyev, Table of n, a(n) for n = 1..430 (first 388 terms from Sean A. Irvine)

Crossrefs

Cf. A112927 (base 2), A143663 (base 3), A112092 (base 4), A143665 (base 5), A379639 (base 6), A379640 (base 7), A379641 (base 8), A379642 (base 9), A007138 (base 10), A379644 (base 11), A252170 (base 12).

Cf. A074249.

Programs

PARI

listap(nn) = {prf = []; for (n=1, nn, vp = (factor(7^n-1)[, 1])~; f = setminus(Set(vp), Set(prf)); prf = concat(prf, f); print1(vecmin(Vec(f)), ", "); ); }