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 A011927 #15 Jul 08 2025 02:42:58 %S A011927 0,0,0,0,1,7,21,49,98,177,296,465,698,1009,1413,1927,2569,3360,4320, %T A011927 5472,6840,8449,10327,12501,15001,17858,21105,24776,28905,33530,38689, %U A011927 44421,50767,57769,65472,73920 %N A011927 [ n(n-1)(n-2)(n-3)/17 ]. %H A011927 <a href="/index/Rec#order_21">Index entries for linear recurrences with constant coefficients</a>, signature (4, -6, 4, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -4, 6, -4, 1). %F A011927 From _Chai Wah Wu_, Aug 02 2020: (Start) %F A011927 a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) + a(n-17) - 4*a(n-18) + 6*a(n-19) - 4*a(n-20) + a(n-21) for n > 20. %F A011927 G.f.: x^4*(-x^16 - 3*x^15 + x^14 - 3*x^13 - x^12 - 2*x^11 - x^10 - 4*x^8 - x^6 - 2*x^5 - x^4 - 3*x^3 + x^2 - 3*x - 1)/(x^21 - 4*x^20 + 6*x^19 - 4*x^18 + x^17 - x^4 + 4*x^3 - 6*x^2 + 4*x - 1). (End) %o A011927 (PARI) a(n)=n*(n-1)*(n-2)*(n-3)\17 \\ _Charles R Greathouse IV_, Oct 18 2022 %K A011927 nonn,easy %O A011927 0,6 %A A011927 _N. J. A. Sloane_