[seqfan] Re: Squares with even-positioned digits matching the original number

[Kevin Ryde]

Tim Peters <tim.peters at gmail.com> writes:
>
> OK - changing the algorithm to build suffixes

I tried the same.  Among lengths <= 22 digits, one further term,
with only about medium confidence of not missing anything.

    8999444174739301478678   length 22

> (very roughly) sqrt(10^k) feasible suffixes.  For k=20
> above, about 4.4 billion were generated.

Yes about 10x more for 2 more digits on a slightly different
measure of how many times reach maximum length without the
pruning stopping it earlier.