A211243 Order of 7 mod n-th prime: least k such that prime(n) divides 7^k-1.

1, 1, 4, 0, 10, 12, 16, 3, 22, 7, 15, 9, 40, 6, 23, 26, 29, 60, 66, 70, 24, 78, 41, 88, 96, 100, 51, 106, 27, 14, 126, 65, 68, 69, 74, 150, 52, 162, 83, 172, 178, 12, 10, 24, 98, 99, 210, 37, 113, 228, 116, 238, 240, 125, 256, 262, 268, 135, 138, 20, 141, 292

Offset: 1

Author

T. D. Noe, Apr 11 2012

Keywords

• nonn
• easy

Links

• T. D. Noe, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A019337 (full reptend primes in base 7).

In other bases: A014664, A062117, A082654, A211241, A211242, A211244, A211245, A002371.

Row lengths of A201911. - Michel Marcus, Feb 04 2019

Programs

GAP

A000040:=Filtered([1..350],IsPrime);;
List([1..Length(A000040)],n->OrderMod(7,A000040[n])); # Muniru A Asiru, Feb 06 2019

Mathematica

nn = 7; Table[If[Mod[nn, p] == 0, 0, MultiplicativeOrder[nn, p]], {p, Prime[Range[100]]}]

PARI

a(n,{base=7}) = my(p=prime(n)); if(base%p, znorder(Mod(base,p)), 0) \\ Jianing Song, May 13 2024