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 produce another whole-number square, even when the equation is not in its simplest form. "Proof": Assume formula_40 is rational. Therefore, But the lemma proves that the sum of two identical whole-number squares cannot produce another whole-number square. Therefore, the assumption that formula_40 is rational is contradicted. formula_40 is irrational. Q. E. D. One-half of , also the reciprocal of , approximately , is a common quantity in geometry and trigonometry because the unit vector that makes a 45° angle with the axes in a plane has the coordinates This number satisfies One interesting property of is as follows: since This