645720631 has 4 divisors (see below), whose sum is σ = 646880472. Its totient is φ = 644560792.

The previous prime is 645720629. The next prime is 645720671. The reversal of 645720631 is 136027546.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 645720631 - 2¹ = 645720629 is a prime.

It is a super-2 number, since 2×645720631² = 833910266598076322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645720601) 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, 579085 + ... + 580198.

It is an arithmetic number, because the mean of its divisors is an integer number (161720118).

Almost surely, 2^645720631 is an apocalyptic number.

645720631 is a deficient number, since it is larger than the sum of its proper divisors (1159841).

645720631 is a wasteful number, since it uses less digits than its factorization.

645720631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1159840.

The product of its (nonzero) digits is 30240, while the sum is 34.

The square root of 645720631 is about 25411.0336468236. The cubic root of 645720631 is about 864.3339146972. Note that the first 3 decimals are identical.

The spelling of 645720631 in words is "six hundred forty-five million, seven hundred twenty thousand, six hundred thirty-one".