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 A216093 #15 Apr 24 2017 18:25:46 %S A216093 5,75,375,9375,9375,109375,7109375,87109375,787109375,1787109375, %T A216093 81787109375,81787109375,81787109375,40081787109375,740081787109375, %U A216093 3740081787109375,43740081787109375,743740081787109375 %N A216093 a(n) = 10^n - (5^(2^n) mod 10^n). %C A216093 a(n)^3 mod 10^n = a(n). %C A216093 a(n) is the unique positive integer less than 10^n such that a(n) is divisible by 5^n and a(n) + 1 is divisible by 2^n. - _Eric M. Schmidt_, Sep 01 2012 %C A216093 a(n+1) + a(n)^2 == 0 (mod 10^(n+1)). - _Robert Israel_, Apr 24 2017 %H A216093 Robert Israel, <a href="/A216093/b216093.txt">Table of n, a(n) for n = 1..999</a> %F A216093 2^(4*5^(n-1)) mod 10^n - 1. %p A216093 f:= n -> (-5 &^(2^n) mod 10^n): %p A216093 map(f, [$1..30]); # _Robert Israel_, Apr 24 2017 %o A216093 (Sage) def A216093(n) : return crt(-1, 0, 2^n, 5^n) # _Eric M. Schmidt_, Sep 01 2012 %Y A216093 Cf. A007185, A016090, A216092, A091663, A018248. %K A216093 nonn %O A216093 1,1 %A A216093 _V. Raman_, Sep 01 2012