644640406 has 4 divisors (see below), whose sum is σ = 966960612. Its totient is φ = 322320202.

The previous prime is 644640349. The next prime is 644640407. The reversal of 644640406 is 604046446.

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

It is a super-2 number, since 2×644640406² = 831122506095689672, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644640407) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 161160100 + ... + 161160103.

It is an arithmetic number, because the mean of its divisors is an integer number (241740153).

Almost surely, 2^644640406 is an apocalyptic number.

644640406 is a deficient number, since it is larger than the sum of its proper divisors (322320206).

644640406 is a wasteful number, since it uses less digits than its factorization.

644640406 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 322320205.

The product of its (nonzero) digits is 55296, while the sum is 34.

The square root of 644640406 is about 25389.7697114409. The cubic root of 644640406 is about 863.8516647424.

The spelling of 644640406 in words is "six hundred forty-four million, six hundred forty thousand, four hundred six".