...=p(1250,2500)=p(2500,5000)=p(5000,10000)
=p(10000,20000)=p(20000,40000)=p(40000,80000)=....

...+p(2500,5000)+p(5000,10000)+p(10000,20000)+p(20000,40000)+...
=|Z|p(10000,20000)
<=1.

p(10000,20000)=0.