Jonathan Post jvospost3 at gmail.com
Sun May 30 16:41:20 CEST 2010

```I'm afraid that when Yahoo deleted 30,000 of my archived emails
without asking my permission, I lost my records of which of several

I'd kept in touch with the wonderful Erich Friedman, but do not have
my notes n why he chooses not to list authors of submitted numbers,
whether or not he keeps such records off-line, and my trying several
times to reconcile his terminology with OEIS.  Fort example, he makes
a different default for "number of prime factors" as to whether or not
that means distinct or with multiplicity.  He is always a delight to
communicate with, and has done fascinating work in many areas.

On Sun, May 30, 2010 at 7:21 AM, Richard Mathar
<mathar at strw.leidenuniv.nl> wrote:
>
> 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
>
>
>
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