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

1,2

Links

Table of n, a(n) for n=1..63.

Prog

(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)

Crossrefs

Cf. A230038.

Sequence in context: A072153 A206929 A331546 * A039025 A326675 A043692

Adjacent sequences: A230057 A230058 A230059 * A230061 A230062 A230063

Keyword

nonn

Author

Ralf Stephan, Oct 08 2013

Status

approved