A054731 Numbers of the form x*(x + 1)*y*(y + 1)/4 where x and y are distinct.

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

Offset

1,2

Links

Table of n, a(n) for n=1..57.

Formula

a(n) = A053990(n) / 4. - Sean A. Irvine, Feb 19 2022

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: A194458 A083266 A334130 * A334129 A282064 A029716

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