A230060 Numbers k such that the distance from k^2 to the smallest triangular number >= k^2 is itself triangular.

1, 3, 5, 6, 7, 9, 11, 15, 18, 20, 28, 30, 35, 42, 45, 54, 60, 63, 66, 77, 78, 88, 90, 102, 105, 114, 117, 126, 130, 138, 150, 162, 165, 174, 175, 186, 198, 204, 210, 221, 222, 234, 245, 246, 247, 258, 264, 266, 270, 282, 294, 306, 315, 318, 330, 342, 351, 354, 366, 368, 378, 385, 390

Offset: 1

Author

Ralf Stephan, Oct 08 2013

Keywords

• nonn

Crossrefs

Cf. A230038.

Programs

PARI

is(n)=my(t=floor((sqrt(8*n^2)-1)/2)+1);t=t*(t+1)/2-n^2; my(tt=floor((sqrt(8*t)-1)/2)+1);(tt*(tt+1)/2==t)