Hi - does anyone know what factor is used by the civil service classic scheme for calculating inverse commutation?

I believe I have a preserved pension of 4,350 pa with a lump sum of 13,050. If I were to ask for that lump sum to be converted to pension, how much would my annual pension be please?

I am 56 next birthday and plan on taking actuarial bought out early retirement three-months after that birthday.

Thanks in advance.