638721 is a `hidden beast` number, since 638 + 7 + 21 = 666.
638721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
It is an alternating number because its digits alternate between even and odd.
It is a Duffinian number.
It is a plaindrome in base 14.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 638721.
2638721 is an apocalyptic number.
It is an amenable number.
638721 is a wasteful number, since it uses less digits than its factorization.
638721 is an evil number, because the sum of its binary digits is even.
The square root of 638721 is about 799.2002252252. The cubic root of 638721 is about 86.1199426098.
The spelling of 638721 in words is "six hundred thirty-eight thousand, seven hundred twenty-one".