644242666 has 16 divisors (see below), whose sum is σ = 998096904. Its totient is φ = 311710464.

The previous prime is 644242661. The next prime is 644242691. The reversal of 644242666 is 666242446.

It can be written as a sum of positive squares in 4 ways, for example, as 643687641 + 555025 = 25371^2 + 745^2 .

It is a super-2 number, since 2×644242666² = 830097225389575112, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644242661) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 33891 + ... + 49366.

Almost surely, 2^644242666 is an apocalyptic number.

644242666 is a deficient number, since it is larger than the sum of its proper divisors (353854238).

644242666 is a wasteful number, since it uses less digits than its factorization.

644242666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 83385.

The product of its digits is 331776, while the sum is 40.

The square root of 644242666 is about 25381.9358205792. The cubic root of 644242666 is about 863.6739640965.

The spelling of 644242666 in words is "six hundred forty-four million, two hundred forty-two thousand, six hundred sixty-six".