Here we have strings in decimal are 2, 4, 6, 10, 14, and so on as (n mod 4 = 2 (n is decimal value)) so here dfa is ending with 10 in binary and it has a minimal state as n+1 for ending with m length string (m is the length of 10 ), as the length of string 10 is 2 so minimal states are 3.