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 modulo n a primitive formula_25-th root of unity because there is the smaller exponent formula_72. That is, by exponentiating "x" one can obtain formula_84 different primitive "k"-th roots of unity, but these may not be all such roots. However, finding all of them is not so easy. You may want to know, in what integer residue class rings you have a primitive "k"-th root of unity. You need it for instance if you want to compute a Discrete Fourier Transform (more precisely a Number theoretic transform) of a formula_25-dimensional integer vector. In order to perform the inverse transform, you also need to