400 (number) third perfect number, a number whose divisors add up to the actual number (1+2+4+8+16+31+62+124+248=496). 497 = 7 × 71, sum of five consecutive primes (89 + 97 + 101 + 103 + 107) 498 = 2 × 3 × 83, sphenic number, untouchable number, admirable number, abundant number A prime number, Chen prime 400 (number) 400 (four hundred) is the natural number following 399 and preceding 401. 400 is the square of 20. 400 is the sum of the powers of 7 from 0 to 3, thus making it a repdigit in base 7 (1111). A circle is divided into
Nth root positive "n"th root, called the principal "n"th root, which is written formula_6. For "n" equal to 2 this is called the principal square root and the "n" is omitted. The "n"th root can also be represented using exponentiation as "x". For even values of "n", positive numbers also have a negative "n"th root, while negative numbers do not have a real "n"th root. For odd values of "n", every negative number "x" has a real negative "n"th root. For example, −2 has a real 5th root, formula_29 but −2 does not have any real 6th roots. Every non-zero number "x",