A098937 Number of cyclic numbers, primes with primitive root 10, (A001913) in the first 10^n primes (A000040).

5, 38, 387, 3755, 37523, 374126, 3740610, 37393725, 373953691, 3739544360

Offset: 1

Author

Robert G. Wilson v, Oct 19 2004

Keywords

• base
• more
• nonn

Crossrefs

Cf. A001913, A006883, A000040, A005596.

Programs

Mathematica

f[n_Integer] := Block[{ds = Divisors[n - 1]}, (n - 1)/Take[ds, Position[ PowerMod[10, ds, n], 1][[1, 1]]][[ -1]]]; c = 0; k = 4; Do[ While[k <= 10^n, a = f[ Prime[k]]; If[a == 1, c++ ]; k++ ]; Print[c], {n, 7}]

Formula

Lim_{n->oo} a(n)/10^n = Artin's constant (A005596).

Extensions

a(8)-a(10) from Amiram Eldar, Jul 04 2021