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 A099179 #19 Feb 16 2025 08:32:54 %S A099179 2,4,20,1540,609896980,37811003218473324699257860, %T A099179 9009555207802177724984164589516456320805205201729086740415363658290866918420 %N A099179 Iterated tetrahedral numbers. %C A099179 The next term, a(8), has 228 digits. - _Harvey P. Dale_, Dec 18 2012 %H A099179 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TetrahedralNumber.html">Tetrahedral Number</a>. %F A099179 a(n)= A000292(a(n-1)). - _R. J. Mathar_, Jun 09 2008 %e A099179 a(2) = Tet(2) = the 2nd tetrahedral number = 2*(2+1)*(2+2)/6 = 4; %e A099179 a(3) = Tet(Tet(2)) = the 4th tetrahedral number = 4*(4+1)*(4+2)/6 = 20; %e A099179 a(4) = Tet(Tet(Tet(2))) = the 20th tetrahedral number = 20*(20+1)*(20+2)/6 = 1540. %t A099179 NestList[(#(#+1)(#+2))/6&,2,6] (* _Harvey P. Dale_, Dec 18 2012 *) %Y A099179 Cf. A007501, A000292. %K A099179 easy,nonn %O A099179 1,1 %A A099179 _Jonathan Vos Post_, Nov 15 2004 %E A099179 Corrected and extended by _R. J. Mathar_, Jun 09 2008