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 A224474 #9 Feb 16 2025 08:33:19 %S A224474 1,51,751,8751,18751,218751,4218751,74218751,574218751,3574218751, %T A224474 63574218751,163574218751,163574218751,80163574218751,480163574218751, %U A224474 7480163574218751,87480163574218751,487480163574218751,5487480163574218751,15487480163574218751 %N A224474 (2*16^(5^n) - 1) mod 10^n: a sequence of trimorphic numbers ending in 1. %C A224474 a(n) is the unique positive integer less than 10^n such that a(n) + 1 is divisible by 2^n and a(n) - 1 is divisible by 5^n. %H A224474 Eric M. Schmidt, <a href="/A224474/b224474.txt">Table of n, a(n) for n = 1..1000</a> %H A224474 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TrimorphicNumber.html">Trimorphic Number</a> %H A224474 <a href="/index/Ar#automorphic">Index entries for sequences related to automorphic numbers</a> %F A224474 a(n) = (2 * A016090(n) - 1) mod 10^n. %o A224474 (Sage) def A224474(n) : return crt(-1, 1, 2^n, 5^n) %Y A224474 Cf. A033819. Corresponding 10-adic number is A063006. The other trimorphic numbers ending in 1 are included in A199685 and A224476. %K A224474 nonn,base %O A224474 1,2 %A A224474 _Eric M. Schmidt_, Apr 07 2013