644363218 has 4 divisors (see below), whose sum is σ = 966544830. Its totient is φ = 322181608.

The previous prime is 644363173. The next prime is 644363219. The reversal of 644363218 is 812363446.

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

It can be written as a sum of positive squares in only one way, i.e., 532363329 + 111999889 = 23073^2 + 10583^2 .

It is a super-2 number, since 2×644363218² = 830407913422631048, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644363219) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 161090803 + ... + 161090806.

Almost surely, 2^644363218 is an apocalyptic number.

644363218 is a deficient number, since it is larger than the sum of its proper divisors (322181612).

644363218 is a wasteful number, since it uses less digits than its factorization.

644363218 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 322181611.

The product of its digits is 82944, while the sum is 37.

The square root of 644363218 is about 25384.3104692643. The cubic root of 644363218 is about 863.7278315472.

The spelling of 644363218 in words is "six hundred forty-four million, three hundred sixty-three thousand, two hundred eighteen".