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 A124264 #7 Dec 12 2024 02:51:46
%S A124264 2,5,20,51,312,740,15000,34125,160720,4988592,180774720,844074000,
%T A124264 27991656000,66264953040
%N A124264 Hilbert-Warren Add Sequence.
%C A124264 Variant of A124261.
%F A124264 Terms generated by solving n x n linear system [H']x = b where b is unity and elements of H' are given by H'[i,j] = (i + j)/(i + j - 1). Sequence term is the denominator of last unknown xn. Numerator is unity for last term for all problem orders examined.
%o A124264 (Maxima) /* [wxMaxima: input start ] */ load("eigen"); order : 4; X : columnvector(makelist(concat(x,i), i, 1, order)); h[i,j] := (i + j)/(i + j - 1); Unity[i,j] := 1; A : genmatrix(h, order, order); A . X; B : genmatrix(Unity, 1, order); A . X = B; Ap : triangularize(A); Ap . X = B; App : invert(Ap); App . B; /* [wxMaxima: input end ] */
%Y A124264 Cf. A124261.
%K A124264 eigen,frac,hard,nonn
%O A124264 1,1
%A A124264 L. Van Warren (van(AT)wdv.com), Oct 23 2006
%E A124264 The author said that this version of the submission was unsatisfactory and set me a better version in email, which may replace this. - _N. J. A. Sloane_, Oct 24 2006