Explanation:
An IPv4 address in dotted decimal format is constructed using binary arithmetic. In binary arithmetic, each bit within a group represents a power of two. Specifically, the first bit in a group represents 2 to the power of 0, the second bit represents 2 to the power of 1, the third bit represents 2 to the power of 2, and so on.
Binary format is simple because each successive bit in a group is exactly twice the value of the previous bit.
The first octet is 128 + 32 + 8 + 4 = 172
The second octet 64 + 32 + 16 + 8 + 2 + 1 = 123
The third octet 8 + 4 + 1 = 13
The fourth octet is 128 + 16 + 8 + 4 + 1 = 157
Reference: https://en.wikipedia.org/wiki/IPv4