MATH CALCULATIONS
While Jaklerat was here for a few days we worked on a few nice puzzles for him and some for me
You will have to combine your math knowledge with these elements to get the answer for the checker
The Puzzle :

The Question :
What is the next element in the above sequence
The Checker :
You can validate your puzzle solution with
certitude.
Sbyybj U, Yv, B, Fp.....? be Ur, O, Ny, Fr.... ?