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

1,1

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)

Prog

(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)), ", "); ); }

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.

Sequence in context: A181870 A070890 A385808 * A385323 A123907 A367971

Adjacent sequences: A379637 A379638 A379639 * A379641 A379642 A379643

Keyword

nonn

Author

Sean A. Irvine, Dec 28 2024

Status

approved