I just got AP20 with difference 53#:

178284683588844176017 + 53#*n, n=0..19

It took me 10 days with 30 64-bit computers (although some of them were
not working all the time). It is really hard to get a progression that
long with terms having more than 64 bits. Frankly, I was loosing hope I
could get it in a reasonable time.

Jarek