Convert to binary, then convert each "block" of 4 binary bits to a hex digit.
For example, consider 179. In binary, this is 10110011. Break this into blocks of 4 from right to left (since there might be leading zeros): 1011 0011. Then convert each of these blocks to a hex digit: b3.
Note: To convert to octal, break the binary representation into blocks of 3 (from right to left): 010 110 011. Then convert each of these blocks to an octal digit: 263.
"We're kind of on the level of crossword puzzle writers... And no one ever goes to them and gives them an award." ~Joe Strummer sscce.org