644987 has 6 divisors (see below), whose sum is σ = 750348. Its totient is φ = 552804.

The previous prime is 644977. The next prime is 644999. The reversal of 644987 is 789446.

It is a happy number.

It is not a de Polignac number, because 644987 - 2⁶ = 644923 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 644987.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644987.

It is not an unprimeable number, because it can be changed into a prime (644977) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 6533 + ... + 6630.

It is an arithmetic number, because the mean of its divisors is an integer number (125058).

2⁶⁴⁴⁹⁸⁷ is an apocalyptic number.

644987 is a deficient number, since it is larger than the sum of its proper divisors (105361).

644987 is a wasteful number, since it uses less digits than its factorization.

644987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13177 (or 13170 counting only the distinct ones).

The product of its digits is 48384, while the sum is 38.

The square root of 644987 is about 803.1108267232. The cubic root of 644987 is about 86.4006454999.

It can be divided in two parts, 644 and 987, that multiplied together give a triangular number (635628 = T₁₁₂₇).

The spelling of 644987 in words is "six hundred forty-four thousand, nine hundred eighty-seven".