664721424 has 80 divisors (see below), whose sum is σ = 1912377600. Its totient is φ = 221065344.

The previous prime is 664721419. The next prime is 664721461. The reversal of 664721424 is 424127466.

664721424 is a `hidden beast` number, since 6 + 647 + 2 + 1 + 4 + 2 + 4 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 218377 + ... + 221399.

It is an arithmetic number, because the mean of its divisors is an integer number (23904720).

Almost surely, 2^664721424 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 664721424, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (956188800).

664721424 is an abundant number, since it is smaller than the sum of its proper divisors (1247656176).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

664721424 is a wasteful number, since it uses less digits than its factorization.

664721424 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3549 (or 3537 counting only the distinct ones).

The product of its digits is 64512, while the sum is 36.

The square root of 664721424 is about 25782.1919936998. The cubic root of 664721424 is about 872.7299739973.

It can be divided in two parts, 66472 and 1424, that added together give a triangular number (67896 = T₃₆₈).

The spelling of 664721424 in words is "six hundred sixty-four million, seven hundred twenty-one thousand, four hundred twenty-four".