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 A151610 #11 Jul 16 2020 13:35:11 %S A151610 0,252,4935,56560,572215,5503260,51377823,469758912,4227854463, %T A151610 37580958940,330712475863,2886218015856,25013889523623, %U A151610 215504279034492,1847179534652655,15762598695784192,133982088914258095,1134907106097349116,9583660007044397799,80704505322479268720 %N A151610 Number of permutations of 7 indistinguishable copies of 1..n arranged in a circle with exactly 2 adjacent element pairs in decreasing order. %H A151610 Andrew Howroyd, <a href="/A151610/b151610.txt">Table of n, a(n) for n = 1..500</a> %H A151610 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (19,-115,241,-208,64). %F A151610 a(n) = n*((7/2)*8^n - 49*n) for n > 1. - _Andrew Howroyd_, May 04 2020 %F A151610 From _Colin Barker_, Jul 16 2020: (Start) %F A151610 G.f.: 7*x^2*(36 + 21*x - 1175*x^2 + 624*x^3 - 192*x^4) / ((1 - x)^3*(1 - 8*x)^2). %F A151610 a(n) = 19*a(n-1) - 115*a(n-2) + 241*a(n-3) - 208*a(n-4) + 64*a(n-5) for n>6. %F A151610 (End) %o A151610 (PARI) a(n) = if(n <= 1, 0, n*(7*8^n/2 - 49*n)) \\ _Andrew Howroyd_, May 04 2020 %o A151610 (PARI) concat(0, Vec(7*x^2*(36 + 21*x - 1175*x^2 + 624*x^3 - 192*x^4) / ((1 - x)^3*(1 - 8*x)^2) + O(x^20))) \\ _Colin Barker_, Jul 16 2020 %Y A151610 Cf. A151583. %K A151610 nonn,easy %O A151610 1,2 %A A151610 _R. H. Hardin_, May 21 2009 %E A151610 Terms a(7) and beyond from _Andrew Howroyd_, May 04 2020