645681620 has 24 divisors (see below), whose sum is σ = 1357110888. Its totient is φ = 258048000.

The previous prime is 645681557. The next prime is 645681637. The reversal of 645681620 is 26186546.

645681620 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 5895184 + 639786436 = 2428^2 + 25294^2 .

It is a Smith number, since the sum of its digits (38) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10580 + ... + 37460.

It is an arithmetic number, because the mean of its divisors is an integer number (56546287).

Almost surely, 2^645681620 is an apocalyptic number.

It is an amenable number.

645681620 is an abundant number, since it is smaller than the sum of its proper divisors (711429268).

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

645681620 is a wasteful number, since it uses less digits than its factorization.

645681620 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28091 (or 28089 counting only the distinct ones).

The product of its (nonzero) digits is 69120, while the sum is 38.

The square root of 645681620 is about 25410.2660356007. The cubic root of 645681620 is about 864.3165081967.

The spelling of 645681620 in words is "six hundred forty-five million, six hundred eighty-one thousand, six hundred twenty".