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 A216156 #22 Feb 21 2024 02:18:40
%S A216156 10,50,500,5000,50000,500000,5000000,50000000,500000000,5000000000,
%T A216156 50000000000,500000000000,5000000000000,50000000000000,
%U A216156 500000000000000,5000000000000000,50000000000000000,500000000000000000
%N A216156 Period of powers of 11 mod 10^n.
%C A216156 Essentially the same as A093143. - _R. J. Mathar_, Sep 06 2012
%C A216156 Also period of squares mod 10^n. - _Mohammed Yaseen_, Apr 18 2023
%H A216156 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (10).
%F A216156 a(n) = 5*10^(n-1), n >= 2.
%e A216156 a(2) = 50 because 11^50 = 11739085287969531650666649599035831993898213898723001 = 1 mod 1000.
%t A216156 Join[{10}, NestList[10*# &, 50, 20]] (* _Paolo Xausa_, Feb 20 2024 *)
%Y A216156 Cf. A001020, A216099.
%K A216156 nonn,base,easy
%O A216156 1,1
%A A216156 _V. Raman_, Sep 02 2012