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 A090220 #10 Mar 15 2018 04:19:54 %S A090220 1,1,1,1,2,10,20,70,560,1680,2800,30800,369600,800800,11211200, %T A090220 168168000,448448000,7623616000,137225088000,434546112000, %U A090220 8690922240000,182509367040000,669201012480000,15391623287040000,369398958888960000 %N A090220 Denominators used in A090219 to compute formula for column sequences of array A078741. %C A090220 The corresponding numerator sequence is N(n) := [1, 6, 3, 1, 3, 3, 1, 3, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1] for n=1..26. %F A090220 a(n) = lcm(seq(denominator(a(n+2, m))), m=1..n)), with the a(n, m) formula of A090219(n, m) but without the 1/b(n-2) factor and lcm denotes the least common multiple of a set of numbers. %F A090220 N(n) := gcd(seq(numerator(a(n+2, m))), m=1..n)), with the a(n, m) formula of A090219(n, m) but without the 1/b(n-2) factor and gcd denotes the greatest common divisor > 1 of a set of numbers. %e A090220 The fifth (k=7) column of A078741 needs in A090219 the factor b(5) := N(5)/a(5)= 3/2. %K A090220 nonn,easy %O A090220 1,5 %A A090220 _Wolfdieter Lang_, Dec 01 2003