645816 has 32 divisors (see below), whose sum is σ = 1641600. Its totient is φ = 211680.

The previous prime is 645803. The next prime is 645833. The reversal of 645816 is 618546.

645816 is a nontrivial binomial coefficient, being equal to C(1137, 2).

It is a congruent number.

It is an unprimeable number.

645816 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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 7 ways as a sum of consecutive naturals, for example, 1515 + ... + 1893.

It is an arithmetic number, because the mean of its divisors is an integer number (51300).

2⁶⁴⁵⁸¹⁶ is an apocalyptic number.

645816 is the 1136-th triangular number.

It is an amenable number.

645816 is an abundant number, since it is smaller than the sum of its proper divisors (995784).

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

645816 is a wasteful number, since it uses less digits than its factorization.

645816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 459 (or 455 counting only the distinct ones).

The product of its digits is 5760, while the sum is 30.

The square root of 645816 is about 803.6267790461. The cubic root of 645816 is about 86.4376464885.

The spelling of 645816 in words is "six hundred forty-five thousand, eight hundred sixteen".