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A128393
Numbers k such that k^2 divides 13^k - 1.
18
1, 2, 3, 4, 6, 12, 14, 20, 28, 42, 60, 68, 84, 140, 183, 204, 220, 340, 366, 406, 420, 476, 660, 732, 812, 942, 1020, 1218, 1428, 1540, 1806, 1860, 1884, 2380, 2436, 2562, 3612, 3660, 3740, 4060, 4620, 5060, 5124, 6594, 7004, 7140, 8420, 9420, 9940, 11220
OFFSET
1,2
LINKS
MATHEMATICA
Join[{1}, Select[Range[12000], PowerMod[13, #, #^2]==1&]] (* Harvey P. Dale, Sep 05 2012 *)
KEYWORD
nonn,less
AUTHOR
Alexander Adamchuk, Mar 01 2007
STATUS
approved