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Number of idempotent 2 X 2 -n..n matrices.
2

%I #6 Oct 18 2016 10:34:47

%S 12,28,44,60,76,108,124,140,156,188,204,236,252,284,316,332,348,380,

%T 396,428,460,492,508,540,556,588,604,636,652,716,732,748,780,812,844,

%U 876,892,924,956,988,1004,1068,1084,1116,1148,1180,1196,1228,1244,1276,1308,1340

%N Number of idempotent 2 X 2 -n..n matrices.

%C Row 2 of A223453.

%H R. H. Hardin, <a href="/A223454/b223454.txt">Table of n, a(n) for n = 1..210</a>

%e Some solutions for n=3

%e ..0..0....0..0....1.-3....3.-3...-2.-3....1..0....0.-3...-2..3....1..0...-1.-2

%e .-1..1...-2..1....0..0....2.-2....2..3...-3..0....0..1...-2..3....1..0....1..2

%Y Cf. A223453.

%K nonn

%O 1,1

%A _R. H. Hardin_, Apr 09 2013