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 A224476 #10 Feb 16 2025 08:33:19 %S A224476 6,1,251,3751,68751,718751,9218751,24218751,74218751,8574218751, %T A224476 13574218751,663574218751,5163574218751,30163574218751, %U A224476 980163574218751,2480163574218751,37480163574218751,987480163574218751,487480163574218751,65487480163574218751 %N A224476 (2*16^(5^n) + (10^n)/2 - 1) mod 10^n: a sequence of trimorphic numbers ending (for n > 1) in 1. %C A224476 a(n) is the unique positive integer less than 10^n such that a(n) + 2^(n-1) + 1 is divisible by 2^n and a(n) - 1 is divisible by 5^n. %H A224476 Eric M. Schmidt, <a href="/A224476/b224476.txt">Table of n, a(n) for n = 1..1000</a> %H A224476 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TrimorphicNumber.html">Trimorphic Number</a> %H A224476 <a href="/index/Ar#automorphic">Index entries for sequences related to automorphic numbers</a> %F A224476 a(n) = (A224474(n) + 10^n/2) mod 10^n. %o A224476 (Sage) def A224476(n) : return crt(2^(n-1)-1, 1, 2^n, 5^n) %Y A224476 Cf. A033819. Converges to the 10-adic number A063006. The other trimorphic numbers ending in 1 are included in A199685 and A224474. %K A224476 nonn,base %O A224476 1,1 %A A224476 _Eric M. Schmidt_, Apr 07 2013