A259745 Triangular numbers representable as x*y+x+y such that x and y are triangular numbers, x>=y>0.

3, 15, 21, 91, 120, 153, 351, 406, 703, 741, 1891, 3081, 3403, 4465, 5151, 5565, 6555, 9453, 9591, 18721, 22791, 23871, 38226, 39903, 46056, 52326, 79401, 85491, 91378, 104653, 159895, 187578, 207690, 222111, 227475, 229503, 266815, 274911, 280875, 326028, 334971, 354903

Offset: 1

Author

Alex Ratushnyak, Jul 04 2015

Keywords

• nonn

Comments

A subsequence of A000217.

Up to 10^12, only 4 terms admit two representations, namely 3081, 22791, 410871 and 1675365. - Giovanni Resta, Jul 19 2015

Examples

			a(1) = 3 = 1*1 + 1 + 1.
a(2) = 15 = 3*3 + 3 + 3.
a(3) = 21 = 10*1 + 10 + 1.
a(4) = 91 = 45*1 + 45 + 1.
a(5) = 120 = 10*10 + 10 + 10.
a(6) = 153 = 6*21 + 6 + 21.
		

Links

• Giovanni Resta, Table of n, a(n) for n = 1..509 (terms < 10^12)

Crossrefs

Cf. A000217, A259746.