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 A011923 #16 Jul 08 2025 02:42:36 %S A011923 0,0,0,0,1,9,27,64,129,232,387,609,913,1320,1848,2520,3360,4393,5649, %T A011923 7155,8944,11049,13504,16347,19617,23353,27600,32400,37800,43848, %U A011923 50593,58089,66387,75544,85617,96664 %N A011923 [ n(n-1)(n-2)(n-3)/13 ]. %H A011923 <a href="/index/Rec#order_17">Index entries for linear recurrences with constant coefficients</a>, signature (4, -6, 4, -1, 0, 0, 0, 0, 0, 0, 0, 0, 1, -4, 6, -4, 1). %F A011923 From _Chai Wah Wu_, Aug 02 2020: (Start) %F A011923 a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) + a(n-13) - 4*a(n-14) + 6*a(n-15) - 4*a(n-16) + a(n-17) for n > 16. %F A011923 G.f.: x^4*(-x^12 - 5*x^11 + 3*x^10 - 6*x^9 - x^7 - 4*x^6 - x^5 - 6*x^3 + 3*x^2 - 5*x - 1)/(x^17 - 4*x^16 + 6*x^15 - 4*x^14 + x^13 - x^4 + 4*x^3 - 6*x^2 + 4*x - 1). (End) %o A011923 (PARI) a(n)=n*(n-1)*(n-2)*(n-3)\13 \\ _Charles R Greathouse IV_, Oct 18 2022 %K A011923 nonn,easy %O A011923 0,6 %A A011923 _N. J. A. Sloane_