Bin : 2진수 ( binary )
Oct : 8진수 ( octal )
Dec : 10진수 ( decimal )
Hex : 16진수 ( hexadecimal )
bin, oct, hex 메서드 사용! Stringprint(bin(21)) >> 0b10101
print(oct(21)) >> 0o25
print(hex(21)) >> 0x15
print(bin(21)[2:]) >> 10101
print(bin(21).count('1') >> 3
int("n", 진수)print(int('0b10101', 2)) >> 21
print(int('0o25', 8))    >> 21
print(int('0x15', 16))   >> 21