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 A158049 #9 Nov 27 2015 00:36:41 %S A158049 720,95760,323885520,520091041680,646101191031120,1426723480107570960, %T A158049 1908953197598354801040,3574028285578402656777360, %U A158049 5645446200753726958758372240,9359837643523957747903959388560 %N A158049 Determinant of power series with alternate signs of gamma matrix with determinant 6!. %C A158049 a(n) = Determinant(A - A^2 + A^3 - A^4 + A^5 - ... - (-1)^n*A^n) %C A158049 where A is the submatrix A(1..7,1..7) of the matrix with factorial determinant %C A158049 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 A158049 G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008. %e A158049 a(1) = Determinant(A) = 6! = 720. %p A158049 seq(Determinant(sum(A^i*(-1)^(i-1),i=1..n)),n=1..30); %Y A158049 Cf. A111490, A158040-A158048. %K A158049 nonn %O A158049 0,1 %A A158049 _Giorgio Balzarotti_ & _Paolo P. Lava_, Mar 11 2009