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 A055877 #3 Mar 30 2012 17:37:51
%S A055877 1,2,5,6,42,43,18626,18627,5798368522871,5798368522872,
%T A055877 194935493755610196550803104551677768964,
%U A055877 194935493755610196550803104551677768965
%N A055877 Least increasing sequence with a(1) = 1 and Hankel transform {1,1,1,1,...}.
%C A055877 Hankel transform {t(n)} of {a(n)} is given by t(n) = Det[{a(1), a(2), ..., a(n)}, {a(2), a(3), ..., a(n+1)}, ..., {a(n), a(n+1), ..., a(2n-1)}].
%e A055877 Given that {a(n)} = {1,2,5,6,a(5),...}, a(5) is seen to be 42 since Det[{1,2,5},{2,5,6},{5,6,42}] = 1, whereas Det[{1,2,5},{2,5,6},{5,6,43}] = 2.
%K A055877 nonn
%O A055877 1,2
%A A055877 _John W. Layman_, Jul 14 2000