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
Square root of 2 Since it is a convergent of the continued fraction representation of the square root of two, any better rational approximation has a denominator not less than 169, since (≈ 1.4142012) is the next convergent with an error of approx. . The rational approximation of the square root of two, , derived from the fourth step in the Babylonian algorithm starting with , is too large by approx. : its square is … This is a table of recent records in calculating digits of A short proof of the irrationality of can be obtained from the rational root theorem, that is,