Syntax: LN(X)
X = a numeric value greater than 0
LN returns the log base e of X. The inverse of LN is the exponentiation function EXP.
Examples:
LN(6) = 1.7917595
LN(EXP(X4)) = 10, where X4 = 10
LN(-1) = Error - LN, domain is x 
0
Excel function: LN