The OEIS is supported by the many generous donors to the OEIS Foundation.
%I #21 Apr 21 2024 10:29:39
%S 1,2,5,25,82,125,625,2525,3125,3362,5905,12625,15625,29525,63125,
%T 78125,137842,147625,188354,255025,315625,375125,390625,738125,
%U 1062625,1275125,1578125,1875625,1953125,2982025,3690625,5313125,5651522,6375625,6973805
%N Numbers k such that k | 9^k + 1.
%H Giovanni Resta, <a href="/A015957/b015957.txt">Table of n, a(n) for n = 1..200</a>
%t Select[Range[7*10^6],PowerMod[9,#,#]==#-1&] (* _Harvey P. Dale_, Apr 21 2024 *)
%Y Solutions to b^k == -1 (mod k): A006521 (b=2), A015949 (b=3), A015950 (b=4), A015951 (b=5), A015953 (b=6), A015954 (b=7), A015955 (b=8), this sequence (b=9), A015958 (b=10), A015960 (b=11), A015961 (b=12), A015963 (b=13), A015965 (b=14), A015968 (b=15), A015969 (b=16).
%Y Column k=9 of A333429.
%K nonn
%O 1,2
%A _Robert G. Wilson v_
%E More terms from _David W. Wilson_