A076768, zeroes of A090302

Don Reble djr at nk.ca
Mon Dec 1 17:54:39 CET 2003

>> Conjecture:  There are finitely many zeros in this sequence. [A090302]
>> Subsidiary Sequence: Indices of zero.

> 1, 36, 105, 171, 210, 216, 325, 351, 406, 	[equals A076768]

It's easy to show, that if X and 2X-1 are both non-prime, then the X'th
triangular number ((X*X+X)/2) is in that sequence. I expect there are
infinitely many such X's, and so the sequence is infinite.

Quickly checking the first 3000 terms, I see that "216" is the only one
which is not such a triangular number. I wonder if there are others.

Don Reble       djr at nk.ca

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