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 A211147 Number of 2 X 2 matrices having all terms in {-n,...,0,...,n} and nonnegative determinant. 1
 1, 57, 377, 1345, 3553, 7737, 14937, 26177, 42945, 66681, 99193, 142209, 198241, 269049, 357593, 466433, 598401, 756281, 944057, 1164289, 1421601, 1719161, 2061081, 2451329, 2895489, 3396729, 3960569, 4591937, 5296289, 6077881 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS It appears that all terms are of the form 8*k + 1. For a guide to related sequences, see A210000. LINKS MATHEMATICA a = -n; b = n; z1 = 30; t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]] c[n_, k_] := c[n, k] = Count[t[n], k] c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 0, m}] Table[c1[n, 2 n^2], {n, 0, z1}] CROSSREFS Cf. A210000. Sequence in context: A038482 A209517 A097200 * A237360 A076459 A268260 Adjacent sequences:  A211144 A211145 A211146 * A211148 A211149 A211150 KEYWORD nonn AUTHOR Clark Kimberling, Apr 03 2012 STATUS approved

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Last modified October 30 03:24 EDT 2020. Contains 338076 sequences. (Running on oeis4.)