[seqfan] Re: Concordance to "What's Special About This Number?"

[Jonathan Post]

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
dozen are my submissions in "What's Special About This Number?"

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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