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A127102
Numbers n such that n^2 divides 8^n-1.
41
1, 7, 889, 2359, 299593, 2033143, 13549249, 42931441, 100170217, 310935751, 685169191, 3606045247, 4566096913, 5452293007, 6620620783, 12721617559, 30987132463, 65576560063, 92349997537, 104785348087, 457967746369
OFFSET
1,2
COMMENTS
Subsequence of A014949.
a(5) = 299593 = (8^7-1)/7 is a repunit in base 8, 1111111(base 8). The first 5 listed terms of a(n) are terms of the finite sequence A003530: divisors of 8^7-1. [Corrected and edited by M. F. Hasler, Nov 21 2018]
Also a subsequence of A177908, see there for more comments on properties of terms of this sequence. - M. F. Hasler, Nov 21 2018
MATHEMATICA
Select[Range[20000], IntegerQ[(PowerMod[8, #, #^2 ]-1)/#^2 ]&]
PROG
(PARI) is(n)=Mod(8, n^2)^n==1 \\ M. F. Hasler, Nov 21 2018
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Jan 05 2007, Jan 07 2007
EXTENSIONS
More terms from Ryan Propper, Jan 05 2007
Terms a(12) onward from Max Alekseyev, May 06 2010
STATUS
approved