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
Root of unity 5th root of unity) is an element of the ring Z[] (). For two pairs of non-real 5th roots of unity these sums are inverse golden ratio and minus golden ratio. For , for any root of unity equals to either 0, ±2, or ± (). For , for any root of unity, equals to either 0, ±1, ±2 or ± (). Root of unity In mathematics, a root of unity, occasionally called a de Moivre number, is any complex number that gives 1 when raised to some positive integer power . Roots of unity are used in many branches