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 A054731 Numbers of the form x*(x + 1)*y*(y + 1)/4 where x and y are distinct. 4
 0, 3, 6, 10, 15, 18, 21, 28, 30, 36, 45, 55, 60, 63, 66, 78, 84, 90, 91, 105, 108, 120, 126, 135, 136, 150, 153, 165, 168, 171, 190, 198, 210, 216, 231, 234, 253, 270, 273, 276, 280, 300, 315, 325, 330, 351, 360, 378, 396, 406, 408, 420, 435, 450, 459, 465, 468 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS MATHEMATICA With[{upto=500}, Select[Union[(#[[1]](#[[1]]+1)#[[2]](#[[2]]+1))/4&/@ Subsets[ Range[0, Floor[upto/2]], {2}]], #<=upto&]] (* Harvey P. Dale, Jan 15 2015 *) CROSSREFS Cf. A053990, A054734. Contains all triangular numbers >1. Sequence in context: A120993 A194458 A083266 * A282064 A029716 A284521 Adjacent sequences:  A054728 A054729 A054730 * A054732 A054733 A054734 KEYWORD nonn,easy AUTHOR Stuart M. Ellerstein (ellerstein(AT)aol.com), Apr 22 2000 EXTENSIONS More terms from James A. Sellers, Apr 22 2000 STATUS approved

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Last modified October 18 07:58 EDT 2018. Contains 316307 sequences. (Running on oeis4.)