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 A120331 #13 Apr 03 2015 19:22:05 %S A120331 1,1,6,72,1776,89280,9065472,1850148864,757046525952,620298979246080, %T A120331 1017126921430892544,3336658943759213395968, %U A120331 21894988380633154342354944,287369531352172835754234347520,7543680108676972971562235527692288 %N A120331 Number of polynomials in two noncommuting variables over the field F_2 having complexity or rank n. %H A120331 R. Bacher, <a href="/A120331/b120331.txt">Table of n, a(n) for n = 0..24</a> %H A120331 R. Bacher, <a href="http://arxiv.org/abs/0804.1092">The special subgroup of invertible non-commutative rational power series as a metric group</a>, arXiv:0804.1092 %F A120331 The reference contains a somewhat complicated formula. %e A120331 The six polynomials corresponding to a(2) are: X, Y, X+Y, 1+X, 1+Y, 1+X+Y. %Y A120331 Cf. A137342. %K A120331 nonn %O A120331 0,3 %A A120331 _Roland Bacher_, Apr 29 2008