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 A133698 #19 Jan 18 2025 10:06:43 %S A133698 1,0,1,0,0,2,0,0,0,1,0,0,0,0,2,0,0,0,0,0,2,0,0,0,0,0,0,2,0,0,0,0,0,0, %T A133698 0,1,0,0,0,0,0,0,0,0,3,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,2,0,0, %U A133698 0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,0,0,2 %N A133698 Triangle, diagonal = A001227 with the rest zeros. %C A133698 Lower triangular part of an infinite matrix with A001227 (number of odd divisors of n) as the main diagonal, and the rest filled with zeros. - Redacted from the original formula given by the author. - _Antti Karttunen_, Jan 18 2025 %H A133698 Antti Karttunen, <a href="/A133698/b133698.txt">Table of n, a(n) for n = 1..22155; the first 210 rows of the triangle</a> %e A133698 First few rows of the triangle are: %e A133698 1; %e A133698 0, 1; %e A133698 0, 0, 2 %e A133698 0, 0, 0, 1; %e A133698 0, 0, 0, 0, 2; %e A133698 0, 0, 0, 0, 0, 2; %e A133698 0, 0, 0, 0, 0, 0, 2; %e A133698 0, 0, 0, 0, 0, 0, 0, 1; %e A133698 0, 0, 0, 0, 0, 0, 0, 0, 3; %e A133698 0, 0, 0, 0, 0, 0, 0, 0, 0, 2; %e A133698 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2; %e A133698 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2; %e A133698 ... %o A133698 (PARI) %o A133698 A000265(n) = (n>>valuation(n,2)); %o A133698 A133698(n) = if(ispolygonal(n,3), numdiv(A000265((sqrtint(1+(n*8))-1)/2)), 0); \\ _Antti Karttunen_, Jan 18 2025 %Y A133698 Cf. A001227, A130209, A133699. %K A133698 nonn,tabl %O A133698 1,6 %A A133698 _Gary W. Adamson_, Sep 21 2007 %E A133698 Offset corrected from 0 to 1 and data section extended to a(105) by _Antti Karttunen_, Jan 18 2025