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 A224477 #8 Feb 16 2025 08:33:19 %S A224477 0,75,125,5625,40625,390625,7890625,62890625,712890625,3212890625, %T A224477 68212890625,418212890625,4918212890625,9918212890625,759918212890625, %U A224477 1259918212890625,6259918212890625,756259918212890625,7256259918212890625,42256259918212890625 %N A224477 (5^(2^n) + (10^n)/2) mod 10^n: a sequence of trimorphic numbers ending (for n > 1) in 5. %C A224477 a(n) is the unique nonnegative integer less than 10^n such that a(n) + 2^(n-1) - 1 is divisible by 2^n and a(n) is divisible by 5^n. %H A224477 Eric M. Schmidt, <a href="/A224477/b224477.txt">Table of n, a(n) for n = 1..1000</a> %H A224477 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TrimorphicNumber.html">Trimorphic Number</a> %H A224477 <a href="/index/Ar#automorphic">Index entries for sequences related to automorphic numbers</a> %F A224477 a(n) = (A007185(n) + 10^n/2) mod 10^n. %o A224477 (Sage) def A224477(n) : return crt(2^(n-1)+1, 0, 2^n, 5^n) %Y A224477 Cf. A033819. Converges to the 10-adic number A018247. The other trimorphic numbers ending in 5 are included in A007185, A216093, and A224478. %K A224477 nonn,base %O A224477 1,2 %A A224477 _Eric M. Schmidt_, Apr 07 2013