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 A015212 #19 May 14 2019 17:57:20
%S A015212 1,2,24,928,224096,180925632,915592324864,15519120649837568,
%T A015212 1649093881865807133696,586980815917441872922703872,
%U A015212 1309843539264798142345101012967424,9790772765676733007363874643686313525248
%N A015212 Sum of Gaussian binomial coefficients for q=21.
%D A015212 J. Goldman and G.-C. Rota, The number of subspaces of a vector space, pp. 75-83 of W. T. Tutte, editor, Recent Progress in Combinatorics. Academic Press, NY, 1969.
%D A015212 I. P. Goulden and D. M. Jackson, Combinatorial Enumeration. Wiley, NY, 1983, p. 99.
%D A015212 M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351.
%H A015212 Vincenzo Librandi, <a href="/A015212/b015212.txt">Table of n, a(n) for n = 0..50</a>
%H A015212 Kent E. Morrison, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL9/Morrison/morrison37.html">Integer Sequences and Matrices Over Finite Fields</a>, Journal of Integer Sequences, Vol. 9 (2006), Article 06.2.1.
%F A015212 a(0) = 1, a(1) = 2, a(n) = 2*a(n-1) + a(n-2)*((21^(n-1)) - 1). - _Vincenzo Librandi_, Nov 02 2012
%t A015212 Total/@Table[QBinomial[n, m, 21], {n, 0, 20}, {m, 0, n}] (* _Vincenzo Librandi_, Nov 02 2012 *)
%Y A015212 Row sums of triangle A022185.
%K A015212 nonn
%O A015212 0,2
%A A015212 _N. J. A. Sloane_, _Olivier Gérard_