Steam Sterilization times related to pressure

Due to budget limitation I’m unable to provide stable 15PSI for longer time.

I came across this formula F0=dt x 10^((T-121)/10). Unfortunately math seems odd with this one. Example provided of 115C gives result of 0.2511 instead of 0.3981 as stated by Ankur. The second result is true for 117C. But then again, this concludes that higher temperatures need longer time…

Shouldn’t the equation be as follows: F0=dt / 10^((T-121)/10) ?