login
A128679
Numbers k such that k^3 divides 5^(k^2) + 1.
20
1, 3, 21, 609, 903, 2667, 9429, 15501, 18543, 26187, 77343, 108507, 114681, 159663, 212541, 273441, 318507, 405447, 537747, 797349, 1197483, 1357503, 1398747, 1731387, 2354961, 3146703, 3325749, 4451181, 4630227, 4665801, 5192943
OFFSET
1,2
COMMENTS
3 divides a(n) for n > 1. 7 divides a(n) for n > 2.
MATHEMATICA
Select[Range[5*10^6], Mod[ 5^(#^2)+1, #^3]==0 &] (* G. C. Greubel, Jan 18 2018 *)
CROSSREFS
Cf. A127263 (numbers k such that k^3 divide 2^(k^2)+1).
Cf. A128677 (least k > p such that (k*p)^3 divides (p-1)^(k*p)^2+1, where p = prime(n) > 2).
Sequence in context: A145386 A344260 A135327 * A292331 A111432 A180999
KEYWORD
hard,nonn
AUTHOR
Alexander Adamchuk, Mar 31 2007
EXTENSIONS
More terms from Ryan Propper, Dec 31 2007
STATUS
approved