This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A277371 #45 Sep 21 2022 11:10:04
%S A277371 1,2,4,5,26,205,2404,88171,1785134,2010899,58796834,639723359,
%T A277371 657788549,2050134685,4809019972,6114530474,11931055777,1292089439947,
%U A277371 1294667166242,4586221808305
%N A277371 Positive integers k that divide 7^k + 3.
%C A277371 No other terms below 10^15. Some larger terms: 68363072121992414, 95409505835353571, 1579273736555455916822694118995172, 5481414795965035698701145369881812, 14905708205837180834697194210878924, 45415365018055454586462673640490785681840279, 147329898999183698422689397719859437775766016038732177717811807964. - _Max Alekseyev_, Oct 18 2016
%F A277371 A066438(a(n)) = a(n) - 3 for n > 2.
%e A277371 7^5 + 3 = 16810 = 5 * 3362, so 5 is a term.
%t A277371 Select[Range[10000], Divisible[7^# + 3, #] &] (* _Alonso del Arte_, Oct 11 2016 *)
%t A277371 Join[{1,2},Select[Range[21*10^5],PowerMod[7,#,#]==#-3&]] (* The program generates the first 10 terms of the sequence. *) (* _Harvey P. Dale_, Sep 21 2022 *)
%o A277371 (PARI) is(n) = Mod(7, n)^n==-3 \\ _Felix Fröhlich_, Oct 14 2016
%Y A277371 Cf. A066438.
%Y A277371 Cf. Solutions to 7^n == k (mod n): this sequence (k=-3), A277370 (k=-2), A015954 (k=-1), A067947 (k=1), A277401 (k=2), A277554 (k=3).
%K A277371 nonn,more
%O A277371 1,2
%A A277371 _Seiichi Manyama_, Oct 11 2016
%E A277371 a(15)-a(20) from _Max Alekseyev_, Oct 18 2016