No one solved last week's riddle yet so here's a small hint.
The answer is 1, but what's the algorithm?
For all those who asked, the prisoners cannot use any special methods
like timing their answers etc... the only information each prisoner can send is a single bit (i.e either black or white) but
that has to also be his guess for the hat.

In the mean while, here's a simple one

what are the next numbers in this series

18, 46, 94, 63, 52, ...