Richard Mathar mathar at strw.leidenuniv.nl
Sun May 30 16:21:04 CEST 2010

```http://list.seqfan.eu/pipermail/seqfan/2010-May/004839.html says

njas> In some cases it may be necessary to create new sequences - see A158304 and A169823 for
njas> examples (if the sequence was not yet in the OEIS).

For 7056, there is an implicit sequence of numbers

"Perfect Squares that are a product of two triangular numbers"
which seems not to be in the OEIS  (?)

0, 1, 9, 36, 100, 225, 441, 784, 900, 1225, 1296, 2025, 3025, 4356, 6084,
7056, 8281, 11025, 14400, 18496, 23409, 29241, 32400, 36100, 44100, 53361,
64009, 76176, 90000, 105625, 123201, 142884, 164836, 189225, 216225,
246016, 278784, 314721, 354025, 396900, 443556, 494209, 549081, 608400,
672400, 741321, 815409, 894916, 980100, 1071225
Superset of A000537.
Cf. A000217
keyword:nonn
offset: 1

This may be refined to a further subset of these,
"Perfect squares which are a product of two distinct triangular numbers"

0, 36, 900, 1225, 7056, 32400, 41616, 44100, 88209, 108900, 298116,
705600, 1368900, 1413721, 1498176, 2924100, 5336100,  8643600, 8820900, 9217296

Examples: 900=3*300. 7056 = 6*1176. 1368900 = 6*228150. 44100 = 36*1225.
Cf. A054731, A000217

RJM

```