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 A145272 #6 Sep 29 2023 19:04:09 %S A145272 1,3,15,210,26565,358999410,64449908117864115, %T A145272 2076895351339769396027702893296360, %U A145272 2156747150208372213435450937462080290024600343143329179374709804540 %N A145272 First differences of successive iterated triangular numbers with seed 2. %C A145272 Also a triangular number -- follows from the definition of A007501. %F A145272 a(n) = T(x(n-1))-x(n-1) where x(n)=T(x(n-1)) and T(x)=x*(x+1)/2. %e A145272 a(1)=T(2)-2. %e A145272 a(2)=T(3)-3. %e A145272 a(3)=T(6)-6. %Y A145272 First differences of successive terms of sequence A007501. %Y A145272 Cf. A000217. %K A145272 easy,nonn %O A145272 1,2 %A A145272 _Greg Huber_, Oct 06 2008