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%I #34 Aug 29 2021 12:01:23
%S 1,3,15,69,2155,34073,876047637,97090036327,420397381695,
%T 2125899832395,3177544777277,34434175473881,40845965389135
%N Positive integers k that divide 7^k + 2.
%C All terms are odd.
%C No other terms below 10^15. Some larger terms: 21419515204636141, 5623143546839445899891, 46186634668308298262543001. - _Max Alekseyev_, Oct 18 2016
%F A066438(a(n)) = a(n) - 2 for n > 1.
%e 7^3 + 2 = 345 = 3 * 115, so 3 is a term.
%t Select[Range[1, 9999, 2], Divisible[7^# + 2, #] &] (* _Alonso del Arte_, Oct 11 2016 *)
%o (PARI) is(n) = Mod(7, n)^n==-2 \\ _Felix Fröhlich_, Oct 14 2016
%Y Cf. A066438.
%Y Cf. Solutions to 7^n == k (mod n): A277371 (k=-3), this sequence (k=-2), A015954 (k=-1), A067947 (k=1), A277401 (k=2), A277554 (k=3).
%K nonn,more
%O 1,2
%A _Seiichi Manyama_, Oct 11 2016
%E a(8)-a(13) from _Max Alekseyev_, Oct 18 2016
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