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 A130209 #13 Jan 17 2025 16:30:25 %S A130209 1,0,2,0,0,2,0,0,0,3,0,0,0,0,2,0,0,0,0,0,4,0,0,0,0,0,0,2,0,0,0,0,0,0, %T A130209 0,4,0,0,0,0,0,0,0,0,3,0,0,0,0,0,0,0,0,0,4,0,0,0,0,0,0,0,0,0,0,2,0,0, %U A130209 0,0,0,0,0,0,0,0,0,6,0,0,0,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,0,0,4 %N A130209 Diagonalized matrix of d(n), A000005, number of divisors of n. %H A130209 Antti Karttunen, <a href="/A130209/b130209.txt">Table of n, a(n) for n = 1..22155; the first 210 rows of the triangle</a> %F A130209 T(n,n) = A000005(n), %F A130209 T(n,k) = 0 if n <> k. %e A130209 First few rows of the triangle are: %e A130209 1; %e A130209 0, 2; %e A130209 0, 0, 2; %e A130209 0, 0, 0, 3; %e A130209 0, 0, 0, 0, 2; %e A130209 0, 0, 0, 0, 0, 4; %e A130209 ... %p A130209 A130209 := proc(n,k) %p A130209 if k = n then %p A130209 numtheory[tau](n); %p A130209 else %p A130209 0; %p A130209 end if; %p A130209 end proc: # _R. J. Mathar_, Aug 06 2016 %o A130209 (PARI) A130209(n) = if(ispolygonal(n,3), numdiv((sqrtint(1+(n*8))-1)/2), 0); \\ _Antti Karttunen_, Jan 17 2025 %Y A130209 Cf. A000005, A130207, A130209. %K A130209 nonn,tabl,easy %O A130209 1,3 %A A130209 _Gary W. Adamson_, May 16 2007 %E A130209 Data section extended up to a(105) by _Antti Karttunen_, Jan 17 2025