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 A224478 #10 Feb 16 2025 08:33:19 %S A224478 0,25,875,4375,59375,609375,2109375,37109375,287109375,6787109375, %T A224478 31787109375,581787109375,5081787109375,90081787109375, %U A224478 240081787109375,8740081787109375,93740081787109375,243740081787109375,2743740081787109375,57743740081787109375 %N A224478 (16^(5^n) + (10^n)/2 - 1) mod 10^n: a sequence of trimorphic numbers ending (for n > 1) in 5. %C A224478 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 A224478 Eric M. Schmidt, <a href="/A224478/b224478.txt">Table of n, a(n) for n = 1..1000</a> %H A224478 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TrimorphicNumber.html">Trimorphic Number</a> %H A224478 <a href="/index/Ar#automorphic">Index entries for sequences related to automorphic numbers</a> %F A224478 a(n) = (A016090(n) + 10^n/2 - 1) mod 10^n. %o A224478 (Sage) def A224478(n) : return crt(2^(n-1)-1, 0, 2^n, 5^n) %Y A224478 Cf. A033819. Converges to the 10-adic number A091663. The other trimorphic numbers ending in 5 are included in A007185, A216093, and A224477. %K A224478 nonn,base %O A224478 1,2 %A A224478 _Eric M. Schmidt_, Apr 07 2013