645981989 has 8 divisors (see below), whose sum is σ = 673139160. Its totient is φ = 619150336.

The previous prime is 645981983. The next prime is 645982013. The reversal of 645981989 is 989189546.

It can be written as a sum of positive squares in 4 ways, for example, as 52085089 + 593896900 = 7217^2 + 24370^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-645981989 is a prime.

It is a super-2 number, since 2×645981989² = 834585460224792242, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645981983) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 77324 + ... + 85269.

It is an arithmetic number, because the mean of its divisors is an integer number (84142395).

Almost surely, 2^645981989 is an apocalyptic number.

It is an amenable number.

645981989 is a deficient number, since it is larger than the sum of its proper divisors (27157171).

645981989 is a wasteful number, since it uses less digits than its factorization.

645981989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 162759.

The product of its digits is 5598720, while the sum is 59.

The square root of 645981989 is about 25416.1757351495. The cubic root of 645981989 is about 864.4505131667.

The spelling of 645981989 in words is "six hundred forty-five million, nine hundred eighty-one thousand, nine hundred eighty-nine".