// isn't a mathematical operator, it's just a conditional operator on mirc meaning "is a factor of", so if (2 // N) checks if N is a multiple of 2
& represents a bitwise comparison, if (N & M), where M is some power of 2, is true if the bit with value M is turned on in N. so if (N & 1) is true if bit with value 1 (the first bit) of N is on, i.e. if its odd
