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 column is a primitive root modulo that number. The columns are labelled with the primes less than 100. The entry in row "p", column "q" is the index of "q" modulo "p" for the given root. For example, in row 11, 2 is given as the primitive root, and in column 5 the entry is 4. This means that 2 = 16 ≡ 5 (mod 11). For the index of a composite number, add the indices of its prime factors.For example, in row 11, the index of 6 is the sum of the indices for 2 and 3: . The