OFFSET
1,1
LINKS
MATHEMATICA
f[n_Integer] := Block[{ds = Divisors[n - 1]}, (n - 1)/Take[ ds, Position[ PowerMod[ 10, ds, n], 1] [[1, 1]]] [[ -1]]]; Select[ Prime[ Range[4, 15000]], f[ # ] == 13 &]
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Robert G. Wilson v, Sep 15 2004
STATUS
approved