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
Primitive root modulo n adding up elements of this multiplicative group? As it happens, sums (or differences) of two primitive roots add up to all elements of the index 2 subgroup of Z/"n" Z for even "n", and to the whole group Z/"n" Z when "n" is odd: No simple general formula to compute primitive roots modulo "n" is known. There are however methods to locate a primitive root that are faster than simply trying out all candidates. If the multiplicative order of a number "m" modulo "n" is equal to formula_2 (the order of Z), then it is a primitive root. In fact