668636640 has 192 divisors, whose sum is σ = 2674667520. Its totient is φ = 152824320.

The previous prime is 668636621. The next prime is 668636653. The reversal of 668636640 is 46636866.

668636640 is a `hidden beast` number, since 6 + 6 + 8 + 636 + 6 + 4 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 19185 + ... + 41295.

It is an arithmetic number, because the mean of its divisors is an integer number (13930560).

Almost surely, 2^668636640 is an apocalyptic number.

668636640 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 668636640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1337333760).

668636640 is an abundant number, since it is smaller than the sum of its proper divisors (2006030880).

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

668636640 is a wasteful number, since it uses less digits than its factorization.

668636640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22142 (or 22128 counting only the distinct ones).

The product of its (nonzero) digits is 746496, while the sum is 45.

The square root of 668636640 is about 25858.0092041131. The cubic root of 668636640 is about 874.4400836883.

The spelling of 668636640 in words is "six hundred sixty-eight million, six hundred thirty-six thousand, six hundred forty".