405 = 34 x 5.
405 has a representation as a sum of two squares: 405 = 92 + 182.
405 is a pentagonal pyramidal number.
405 is 120000 in base 3 and 12111 in base 4. It is 500 in base 9.
405 is a tridecagonal number.
405 is the telephone area code for central Oklahoma.
