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 A064276 #4 May 10 2013 12:44:52
%S A064276 1,5,13,25,42,62,90,118,155,195,243,287,352,404,472,548,629,697,797,
%T A064276 873,986,1094,1202,1294,1443,1559,1687,1823,1984,2100,2296,2420,2597,
%U A064276 2769,2937,3125,3366,3514,3702,3906,4167,4331,4611,4783,5040,5320,5548
%N A064276 Number of 2 X 2 singular integer matrices with elements from {0,...,n} up to row and column permutation.
%F A064276 a(n) = (A059306(n)+(n+1)*(2*n+3))/4.
%e A064276 There are 5 binary singular matrices up to row and column permutation:
%e A064276 [0 0] [1 0] [1 1] [1 0] [1 1]
%e A064276 [0 0] [0 0] [0 0] [1 0] [1 1].
%Y A064276 Cf. A059306, A062801, A059976.
%K A064276 nonn
%O A064276 0,2
%A A064276 _Vladeta Jovovic_, Sep 24 2001
%E A064276 More terms from _David Wasserman_, Jul 16 2002