645640320 has 128 divisors (see below), whose sum is σ = 2216370240. Its totient is φ = 158920704.

The previous prime is 645640249. The next prime is 645640351. The reversal of 645640320 is 23046546.

It is a tau number, because it is divible by the number of its divisors (128).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12027 + ... + 37893.

Almost surely, 2^645640320 is an apocalyptic number.

645640320 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 645640320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1108185120).

645640320 is an abundant number, since it is smaller than the sum of its proper divisors (1570729920).

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

645640320 is a wasteful number, since it uses less digits than its factorization.

645640320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25902 (or 25890 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 30.

The square root of 645640320 is about 25409.4533589371. The cubic root of 645640320 is about 864.2980795926.

Adding to 645640320 its reverse (23046546), we get a palindrome (668686866).

The spelling of 645640320 in words is "six hundred forty-five million, six hundred forty thousand, three hundred twenty".