645547521 has 4 divisors (see below), whose sum is σ = 860730032. Its totient is φ = 430365012.

The previous prime is 645547489. The next prime is 645547531. The reversal of 645547521 is 125745546.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 645547521 - 2⁵ = 645547489 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 645547521.

It is not an unprimeable number, because it can be changed into a prime (645547531) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 107591251 + ... + 107591256.

It is an arithmetic number, because the mean of its divisors is an integer number (215182508).

Almost surely, 2^645547521 is an apocalyptic number.

It is an amenable number.

645547521 is a deficient number, since it is larger than the sum of its proper divisors (215182511).

645547521 is a wasteful number, since it uses less digits than its factorization.

645547521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 215182510.

The product of its digits is 168000, while the sum is 39.

The square root of 645547521 is about 25407.6272209744. The cubic root of 645547521 is about 864.2566685891.

The spelling of 645547521 in words is "six hundred forty-five million, five hundred forty-seven thousand, five hundred twenty-one".