645515649 has 21 divisors (see below), whose sum is σ = 968860339. Its totient is φ = 429886440.

The previous prime is 645515639. The next prime is 645515657. The reversal of 645515649 is 946515546.

The square root of 645515649 is 25407.

It is a perfect power (a square), and thus also a powerful number.

645515649 is a `hidden beast` number, since 6 + 4 + 551 + 56 + 49 = 666.

It can be written as a sum of positive squares in only one way, i.e., 400280049 + 245235600 = 20007^2 + 15660^2 .

It is not a de Polignac number, because 645515649 - 2⁵ = 645515617 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (645515609) by changing a digit.

It is a polite number, since it can be written in 20 ways as a sum of consecutive naturals, for example, 685519 + ... + 686459.

Almost surely, 2^645515649 is an apocalyptic number.

645515649 is the 25407-th square number.

645515649 is the 12704-th centered octagonal number.

It is an amenable number.

645515649 is a deficient number, since it is larger than the sum of its proper divisors (323344690).

645515649 is an frugal number, since it uses more digits than its factorization.

645515649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1900 (or 944 counting only the distinct ones).

The product of its digits is 648000, while the sum is 45.

The cubic root of 645515649 is about 864.2424449826.

The spelling of 645515649 in words is "six hundred forty-five million, five hundred fifteen thousand, six hundred forty-nine".