[seqfan] In search of a formula for a number triangle

Alonso Del Arte alonso.delarte at gmail.com
Mon Jan 7 23:39:34 CET 2013


The triangle of A077341

1

2 20

3 30 31

4 40 41 42

5 50 51 52 53

...

 19 190 191 ...

200 201 202 ...

 21 210 211 ...

...

and the related sequence A077342, initial rows of the triangle, has the
question "Can anyone derive a formula for a(n)?" I can't, but I believe I
may at least be able to figure out which a(n) = n. This is what I've come
up with:

a(n) = n when n > 10 * floor(n/10) + floor(n/10) - 2.

But of course this only takes into account the nearest previous row that
could possibly contain n. Is that enough or does this formula need to be
amended to take into account even earlier rows?

Al



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