645581664 has 720 divisors, whose sum is σ = 2627922528. Its totient is φ = 153280512.

The previous prime is 645581659. The next prime is 645581669. The reversal of 645581664 is 466185546.

645581664 is a `hidden beast` number, since 6 + 4 + 5 + 581 + 6 + 64 = 666.

645581664 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (645581659) and next prime (645581669).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645581669) by changing a digit.

It is a polite number, since it can be written in 119 ways as a sum of consecutive naturals, for example, 28068757 + ... + 28068779.

Almost surely, 2^645581664 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 645581664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1313961264).

645581664 is an abundant number, since it is smaller than the sum of its proper divisors (1982340864).

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

645581664 is a wasteful number, since it uses less digits than its factorization.

645581664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 89 (or 65 counting only the distinct ones).

The product of its digits is 691200, while the sum is 45.

The square root of 645581664 is about 25408.2991166272. The cubic root of 645581664 is about 864.2719051618.

The spelling of 645581664 in words is "six hundred forty-five million, five hundred eighty-one thousand, six hundred sixty-four".