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 A027849 #12 Jul 08 2025 17:56:26 %S A027849 1,20,87,232,485,876,1435,2192,3177,4420,5951,7800,9997,12572,15555, %T A027849 18976,22865,27252,32167,37640,43701,50380,57707,65712,74425,83876, %U A027849 94095,105112,116957,129660,143251 %N A027849 a(n) = (n+1)*(5*n^2+4*n+1). %F A027849 From _Chai Wah Wu_, Jun 10 2016: (Start) %F A027849 a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n > 3. %F A027849 G.f.: (13*x^2 + 16*x + 1)/(x - 1)^4. (End) %Y A027849 Cf. A260260 (comment). [_Bruno Berselli_, Jul 22 2015] %K A027849 nonn,easy %O A027849 0,2 %A A027849 _N. J. A. Sloane_