215
 

215 is 10 mod 41
let be log the log base 10

log(215)=2.33243...


a valid approximation to log(215) is (41*233+10)/(41*10^2)


why?


215*10 is 1 mod 307

1763 mod 307 is 228

228 is about 10^2*log(215)-215/41