645994566 has 96 divisors (see below), whose sum is σ = 1696032000. Its totient is φ = 173586240.

The previous prime is 645994549. The next prime is 645994571. The reversal of 645994566 is 665499546.

645994566 is a `hidden beast` number, since 6 + 4 + 599 + 45 + 6 + 6 = 666.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 355801 + ... + 357611.

It is an arithmetic number, because the mean of its divisors is an integer number (17667000).

Almost surely, 2^645994566 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 645994566, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (848016000).

645994566 is an abundant number, since it is smaller than the sum of its proper divisors (1050037434).

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

645994566 is a wasteful number, since it uses less digits than its factorization.

645994566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1994 (or 1991 counting only the distinct ones).

The product of its digits is 6998400, while the sum is 54.

The square root of 645994566 is about 25416.4231551176. The cubic root of 645994566 is about 864.4561232940.

It can be divided in two parts, 6459 and 94566, that added together give a triangular number (101025 = T₄₄₉).

The spelling of 645994566 in words is "six hundred forty-five million, nine hundred ninety-four thousand, five hundred sixty-six".