Pidyon Haben Riddle Solved

This Bechor needs no Pidyon Haben because his father is alive.

Should his father die then the son needs to redeem himself. 

Shulchan Aruch Y.D. 305:19

A כהן who had a son a בכור who was a חלל 

(son the חלל loses his status as a  כהן)  

If  the father dies within* 30 days of his son's

birth then the son needs to redeem himself.

While the father is alive, as a כהן he is זוכה for 

himself the money. (No Pidyon necessary)

 One reader wrote of another possibility

If the father had only 5 סלעים and both father

and son are Bechorim then the father has

to redeem himself before redeeming his son.

*If the father dies (after 30 days) then the

son puts aside 5 סלעים  he doesn't hand it over 

to a Kohen but gets to keep it.