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 A125119 #4 Feb 16 2025 08:33:04 %S A125119 1,13,341,19531,2015539,329554457,78536544841,25736391511831, %T A125119 11111111111111111,6115909044841454629,4182283628124518315101, %U A125119 3479492117784426363920483,3461445831219105624193478971 %N A125119 Values of repunits with odd length L in base (L+3)/2 representation. %C A125119 Central terms of the triangle in A125118: a(n)=A125118(2*n-1,n). %H A125119 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Repunit.html">Repunit</a> %F A125119 a(n) = Sum((n+1)^k: 0<=k<=2*(n-1)). %e A125119 a(4) = [1111111]_5 = (((((5+1)*5+1)*5+1)*5+1)*5+1)*5+1 = 19531. %K A125119 nonn,base %O A125119 1,2 %A A125119 _Reinhard Zumkeller_, Nov 21 2006