cp's OEIS Frontend

A211142 Number of 2 X 2 matrices having all terms in {-n,...,0,...,n} and determinant n+1.

%I A211142 #9 Jul 25 2017 17:13:10
%S A211142 0,4,24,116,128,408,296,788,748,1232,888,2488,1312,2568,2664,3860,
%T A211142 2352,5652,3032,6864,5320,6456,4520,12152,6356,9264,9000,13288,7392,
%U A211142 18440,8520,17556,13576,16032,14216,28612
%N A211142 Number of 2 X 2 matrices having all terms in {-n,...,0,...,n} and determinant n+1.
%C A211142 For a guide to related sequences, see A210000.
%H A211142 Chai Wah Wu, <a href="/A211142/b211142.txt">Table of n, a(n) for n = 0..3000</a>
%t A211142 a = -n; b = n; z1 = 35;
%t A211142 t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
%t A211142 c[n_, k_] := c[n, k] = Count[t[n], k]
%t A211142 Table[c[n, n + 1], {n, 0, z1}]   (* A211142 *)
%t A211142 %/4                              (* integers *)
%Y A211142 Cf. A210000.
%K A211142 nonn
%O A211142 0,2
%A A211142 _Clark Kimberling_, Apr 03 2012