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 A055865 #9 Aug 07 2025 06:17:26 %S A055865 0,2,12,100,1080,14406,229376,4251528,90000000,2143588810,56757583872, %T A055865 1654301902188,52644347205632,1816448730468750,67553994410557440, %U A055865 2694045224950414864,114692890480116793344,5191945444217181018258,249036800000000000000000,12617615847934310595791220 %N A055865 Second column of triangle A055864. %H A055865 Paolo Xausa, <a href="/A055865/b055865.txt">Table of n, a(n) for n = 1..350</a> %H A055865 Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas for Some Functions on Finite Sets</a> %F A055865 a(1) = 0; a(n) = n*(n+1)^(n-2), n >= 2. %F A055865 E.g.f.: -1/2*(-W(-x)^2+x^2)/x, W(x) principal branch of Lambert's function. %F A055865 a(n) = A055864(n, 2). %t A055865 A055865[n_] := If[n == 1, 0, n*(n+1)^(n-2)]; %t A055865 Array[A055865, 25] (* _Paolo Xausa_, Aug 07 2025 *) %Y A055865 Cf. A055864, A000272, A055858. %K A055865 nonn,easy %O A055865 1,2 %A A055865 _Wolfdieter Lang_ Jun 20 2000