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 A158040 #23 Nov 26 2015 00:20:58 %S A158040 2,32,258,1664,9710,53664,286762,1497600,7691238,38995360,195696226, %T A158040 973894272,4812812446,23642953376,115552680090,562240972800, %U A158040 2724987988054,13161369525408,63371643947474,304287501281920,1457424739149582,6964697175476128 %N A158040 Determinant of power series of gamma matrix with determinant 2!. %C A158040 a(n) = Determinant(A + A^2 + A^3 + A^4 + A^5 + ... + A^n) where A is the submatrix A(1..3,1..3) of the matrix with factorial determinant A = [[1,1,1,1,1,1,...],[1,2,1,2,1,2,...], [1,2,3,1,2,3,...], [1,2,3,4,1,2,...], [1,2,3,4,5,1,...], [1,2,3,4,5,6,...], ...]; note: Determinant A(1..n,1..n) = (n-1)!. %D A158040 G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008. %F A158040 Empirical g.f.: 2*x*(8*x^6 -50*x^4 +64*x^3 -25*x^2 +1) / ((x -1)^2*(2*x -1)^2*(2*x^2 -5*x +1)^2). - _Colin Barker_, Jul 13 2014 %e A158040 a(1) = Determinant(A) = 2! = 2. %p A158040 seq(Determinant(sum(A2^i,i=1..n)),n=1..30); %o A158040 (PARI) vector(100, n, matdet(sum(k=1, n, [1,1,1 ; 1,2,1 ; 1,2,3]^k))) \\ _Colin Barker_, Jul 13 2014 %Y A158040 Cf. A111490. %K A158040 nonn %O A158040 1,1 %A A158040 _Giorgio Balzarotti_ & _Paolo P. Lava_, Mar 11 2009 %E A158040 More terms, and offset changed to 1 by _Colin Barker_, Jul 13 2014