A273614 Numbers k such that 3k - 1 divides 3^k - 1.

1, 9, 12, 96, 345, 432, 852, 945, 1452, 2160, 3480, 3753, 4800, 6561, 6984, 13230, 15840, 17040, 30210, 31008, 40320, 43776, 44352, 44652, 47628, 55200, 56940, 60420, 61065, 69312, 71145, 74100, 77400, 81504, 125580, 128016, 175952, 192240, 198168

Offset: 1

Author

Juri-Stepan Gerasimov, May 26 2016

Keywords

• nonn

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (first 1000 terms from Alois P. Heinz)

Crossrefs

Cf. A024023, A081856, A233415.

Programs

Magma

[n: n in [1..200000] | Modexp(3, n, 3*n-1) eq 1];

Maple

a:= proc(n) option remember; local k;
      if n=1 then 1 else for k from 1+a(n-1)
      while 3&^k mod(3*k-1)<>1 do od; k fi
    end:
seq(a(n), n=1..40);  # Alois P. Heinz, May 27 2016

Mathematica

Select[Range[10^6], PowerMod[3, #, 3*# - 1] == 1 &] (* Giovanni Resta, May 27 2016 *)

PARI

is(n)=Mod(3,3*n-1)^n==1 \\ Charles R Greathouse IV, May 29 2016