645721425 has 18 divisors (see below), whose sum is σ = 1156559222. Its totient is φ = 344384640.

The previous prime is 645721399. The next prime is 645721457. The reversal of 645721425 is 524127546.

It is a happy number.

645721425 is a `hidden beast` number, since 64 + 572 + 1 + 4 + 25 = 666.

It can be written as a sum of positive squares in 3 ways, for example, as 8714304 + 637007121 = 2952^2 + 25239^2 .

It is not a de Polignac number, because 645721425 - 2⁵ = 645721393 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 645721425.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 1434712 + ... + 1435161.

Almost surely, 2^645721425 is an apocalyptic number.

It is an amenable number.

645721425 is a deficient number, since it is larger than the sum of its proper divisors (510837797).

645721425 is a wasteful number, since it uses less digits than its factorization.

645721425 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2869889 (or 2869881 counting only the distinct ones).

The product of its digits is 67200, while the sum is 36.

The square root of 645721425 is about 25411.0492699534. The cubic root of 645721425 is about 864.3342689684.

The spelling of 645721425 in words is "six hundred forty-five million, seven hundred twenty-one thousand, four hundred twenty-five".