OFFSET
1,2
COMMENTS
All terms are odd.
No other terms below 10^15. Some larger terms: 181204957971619289, 21305718571846184078167, 157*(7^157-2)/1355 (132 digits). - Max Alekseyev, Oct 18 2016
FORMULA
A066438(a(n)) = 2 for n > 1.
EXAMPLE
7 == 2 mod 1, so 1 is a term;
16807 == 2 mod 5, so 5 is a term.
MATHEMATICA
Join[{1}, Select[Range[5173*10^5], PowerMod[7, #, #]==2&]] (* The program will generate the first 10 terms of the sequence; it would take a very long time to generate the 11th term. *) (* Harvey P. Dale, Apr 15 2020 *)
PROG
(PARI) isok(n) = Mod(7, n)^n == 2; \\ Michel Marcus, Oct 13 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Seiichi Manyama, Oct 13 2016
EXTENSIONS
a(10) from Michel Marcus, Oct 13 2016
a(11) from Max Alekseyev, Oct 18 2016
STATUS
approved