645981768 has 24 divisors (see below), whose sum is σ = 1749534150. Its totient is φ = 215327232.

The previous prime is 645981761. The next prime is 645981769. The reversal of 645981768 is 867189546.

It can be written as a sum of positive squares in only one way, i.e., 542796804 + 103184964 = 23298^2 + 10158^2 .

It is a tau number, because it is divible by the number of its divisors (24).

It is a super-3 number, since 3×645981768³ (a number of 27 digits) contains 333 as substring.

It is a hoax number, since the sum of its digits (54) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (645981761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4485913 + ... + 4486056.

Almost surely, 2^645981768 is an apocalyptic number.

It is an amenable number.

645981768 is an abundant number, since it is smaller than the sum of its proper divisors (1103552382).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

645981768 is a wasteful number, since it uses less digits than its factorization.

645981768 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8971981 (or 8971974 counting only the distinct ones).

The product of its digits is 2903040, while the sum is 54.

The square root of 645981768 is about 25416.1713875241. The cubic root of 645981768 is about 864.4504145863.

It can be divided in two parts, 64598 and 1768, that added together give a palindrome (66366).

The spelling of 645981768 in words is "six hundred forty-five million, nine hundred eighty-one thousand, seven hundred sixty-eight".