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 A237530 Number of non-equivalent (mod D_3) ways to choose three points in an n X n X n triangular grid so that they do not form a 2 X 2 X 2 subtriangle. 1
 0, 4, 22, 82, 231, 566, 1216, 2410, 4428, 7712, 12780, 20392, 31409, 47032, 68594, 97878, 136836, 187998, 254100, 338602, 445213, 578524, 743424, 945860, 1192126, 1489768, 1846734, 2272430, 2776725, 3371170, 4067840, 4880734, 5824442, 6915732, 8172036, 9613236 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 COMMENTS Without the restriction "non-equivalent (mod D_3)" the numbers are given by A234250. LINKS Heinrich Ludwig, Table of n, a(n) for n = 2..1000 Index entries for linear recurrences with constant coefficients, signature (3,0,-7,3,6,0,-6,-3,7,0,-3,1) FORMULA a(n) = (n^6 + 3*n^5 - 3*n^4 + 10*n^3 - 48*n^2 + IF(n==1 mod 2)*(27*n^2 - 45*n - 9) + IF(n==1 mod 3)*64)/288. G.f.: x^3*(x^7-x^6-2*x^5-15*x^4-13*x^3-16*x^2-10*x-4) / ((x-1)^7*(x+1)^3*(x^2+x+1)). - Colin Barker, Feb 14 2014 CROSSREFS Cf. A234250, A234247. Sequence in context: A201127 A259709 A078155 * A096167 A060453 A038382 Adjacent sequences:  A237527 A237528 A237529 * A237531 A237532 A237533 KEYWORD nonn,easy AUTHOR Heinrich Ludwig, Feb 13 2014 STATUS approved

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Last modified September 28 02:07 EDT 2020. Contains 337392 sequences. (Running on oeis4.)