Let the number of contestants be n

A voter can vote for 1,2, 3, ... n-1 candidates

Number of ways he can vote is

C₁ + C₂ + .. C_n-1 Where C_r  is number of ways of choosing r objects from a total of n..

This is equal to 62

2^n - 2 = 62

2^n = 64

n = 6