It is a bit daft but makes heavy use of the digit 5 and an exclamation mark....:
5! + exp( i pi ) x sum_{ 0<n<=5} ( 1 + n + n^2 ) + 5
I like the factorial sign ! : 5 ! = 5 x 4 x 3 x 3 x 1 = 120
exp ( i pi ) = -1 is
Euler's identity, one of the beautiful formula in mathematics
sum_{0<n<=5} ( 1 + n + n^2 ) = (1 + 1 + 1 ) + ( 1 + 2 + 4 ) + ( 1 + 3 + 9 ) + ( 1 + 4 + 16 ) + ( 1 + 5 + 25 )
= 3 + 7 + 13 + 21 + 31 = 75
so the formula is 120 - 75 + 5 = 50
