A167797 - OEIS

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

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OFFSET

1,1

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

MATHEMATICA

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

PROG

(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

CROSSREFS

Cf. A001913 (primes with primitive root 10)

Sequence in context: A323746 A101240 A191070 * A001913 A270387 A071845

Adjacent sequences: A167794 A167795 A167796 * A167798 A167799 A167800

KEYWORD

nonn

AUTHOR

T. D. Noe, Nov 12 2009

STATUS

approved