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
Triangular number 4 years would lose of its "losable" value in the first year, in the second, in the third, and in the fourth, accumulating a total depreciation of (the whole) of the losable value. By analogy with the square root of , one can define the (positive) triangular root of as the number such that : which follows immediately from the quadratic formula. So an integer is triangular if and only if is a square. Equivalently, if the positive triangular root of is an integer, then is the th triangular number. Triangular number A triangular number or triangle number counts objects