A167797 Numbers with primitive root 10.

7, 17, 19, 23, 29, 47, 49, 59, 61, 97, 109, 113, 131, 149, 167, 179, 181, 193, 223, 229, 233, 257, 263, 269, 289, 313, 337, 343, 361, 367, 379, 383, 389, 419, 433, 461, 487, 491, 499, 503, 509, 529, 541, 571, 577, 593, 619, 647, 659, 701, 709, 727, 743, 811

Offset: 1

Author

T. D. Noe, Nov 12 2009

Keywords

• nonn

Comments

Numbers n such that the decimal expansion of 1/n has period phi(n). For example, 1/49 has period 42.

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A001913 (primes with primitive root 10)

Programs

Mathematica

pr=10; Select[Range[2,2000], MultiplicativeOrder[pr,# ] == EulerPhi[ # ] &]

PARI

is(n)=if(gcd(n, 10)>1, return(0)); my(p=eulerphi(n)); znorder(Mod(10, n), p)==p \\ Charles R Greathouse IV, Jan 04 2025