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%I #28 Oct 07 2017 22:39:20
%S 1,3,9,21,39,63,117,273,819,2067,3081,6201,9243,12807,14469,21567,
%T 43407,48711,50877,64701,89649,146133,149331,163293,166491,221169,
%U 340977,356139,447993,489879,546819,661401,663507,1022931,1143051,1165437,1548183,1639911,1640457
%N Numbers n such that n^2 divides (17^n + 1).
%C After a(1), all the terms are multiples of 3.
%C From _Robert Israel_, Sep 18 2017: (Start)
%C All terms are odd.
%C If m and n are terms then lcm(m,n) is a term.
%C If n is a term not divisible by 9, then 3n is a term. (End)
%e 3 appears is a term because 3^2 divides (17^3 + 1): 4914/9 = 546.
%e 9 appears is a term because 9^2 divides (17^9 + 1): 118587876498/81 = 1464047858.
%p A292392:= proc(n) if(17 &^ n+1)mod (n^2)=0 then RETURN (n); fi; end: seq(A292392(n), n=1..50000);
%t Select[Range[50000], IntegerQ[(PowerMod[17, #, #^2] + 1)/#^2] &]
%o (PARI) for(n=1, 5e6, if (Mod(17, n^2)^n==-1, print1(n, ", ")));
%o (PARI) is(n) = Mod(17, n^2)^n==-1 \\ _Felix Fröhlich_, Sep 16 2017
%Y Cf. A015951, A123047, A123052, A177813, A292331.
%K nonn
%O 1,2
%A _K. D. Bajpai_, Sep 15 2017
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