A037066 a(n)-th prime is the smallest prime containing exactly n 7's.

1, 4, 59, 275, 4924, 58623, 506877, 4546755, 30224014, 87818618, 2836649805, 14748299309, 251285857122, 603200604933, 17530836835060, 80446298927642, 2054098188682332, 9577010472498628, 67026825574168206, 1605887402218872982, 16520076587958693329, 156502536697199220470

Offset: 0

Author

Patrick De Geest, Jan 04 1999

Keywords

• nonn
• base
• hard

Links

• Andrew R. Booker, The Nth Prime Page.
• Kim Walisch, primecount, Fast prime counting function library.

Crossrefs

Cf. A000720, A037067, A034388.

Cf. A037052, A037054, A037056, A037058, A037060, A037062, A037064, A037068, A037070.

Programs

Mathematica

(* see A037067 for f *) PrimePi[ Table[ f[n, 7], {n, 1, 12}]]

Formula

a(n) = A000720(A037067(n)). - Amiram Eldar, Jul 21 2025

Extensions

a(0)=1 prepended by Sean A. Irvine, Dec 06 2020

a(14)-a(21) calculated using Kim Walisch's primecount and added by Amiram Eldar, Jul 21 2025