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 A059306 Number of 2 X 2 singular integer matrices with elements from {0,...,n}. 18
 1, 10, 31, 64, 113, 170, 255, 336, 449, 570, 719, 848, 1057, 1210, 1423, 1664, 1921, 2122, 2447, 2672, 3041, 3386, 3727, 4000, 4497, 4858, 5263, 5696, 6225, 6570, 7231, 7600, 8177, 8730, 9263, 9872, 10689, 11130, 11727, 12384, 13265, 13754, 14703 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Vincenzo Librandi and Chai Wah Wu, Table of n, a(n) for n = 0..10000 (terms for n = 0..100 from Vincenzo Librandi) FORMULA a(n) = A134506(n) + (2n+1)^2. Shi's result (see formula section in A134506) shows that a(n) = kn^2 log n + cn^2 + O(n^e) where k = 12/Pi^2, e > 547/416 = 1.3149..., and c = 4.5113... - Chai Wah Wu, Nov 28 2016 MATHEMATICA a[0] = 1; a[n_] := Table[{w, x, y, z} /. {ToRules[ Reduce[0 <= x <= n && 0 <= y <= n && 0 <= z <= n && w*z - x*y == 0, {x, y, z}, Integers]] }, {w, 0, n}] // Flatten[#, 1]& // Length; Table[Print[an = a[n]]; an, {n, 0, 42}] (* Jean-François Alcover, Oct 11 2013 *) CROSSREFS Cf. A062801, A134506. Sequence in context: A211013 A085473 A051943 * A192023 A219693 A297507 Adjacent sequences:  A059303 A059304 A059305 * A059307 A059308 A059309 KEYWORD nonn,nice AUTHOR John W. Layman, Jan 25 2001 EXTENSIONS More terms from Larry Reeves (larryr(AT)acm.org), Jan 09 2003 STATUS approved

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Last modified October 22 18:50 EDT 2019. Contains 328319 sequences. (Running on oeis4.)