644278216 has 8 divisors (see below), whose sum is σ = 1208021670. Its totient is φ = 322139104.

The previous prime is 644278207. The next prime is 644278249. The reversal of 644278216 is 612872446.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 543356100 + 100922116 = 23310^2 + 10046^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a super-2 number, since 2×644278216² = 830188839224285312, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40267381 + ... + 40267396.

Almost surely, 2^644278216 is an apocalyptic number.

It is an amenable number.

644278216 is a deficient number, since it is larger than the sum of its proper divisors (563743454).

644278216 is a wasteful number, since it uses less digits than its factorization.

644278216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80534783 (or 80534779 counting only the distinct ones).

The product of its digits is 129024, while the sum is 40.

The square root of 644278216 is about 25382.6361121141. The cubic root of 644278216 is about 863.6898499556.

The spelling of 644278216 in words is "six hundred forty-four million, two hundred seventy-eight thousand, two hundred sixteen".