645407281 has 4 divisors (see below), whose sum is σ = 661148964. Its totient is φ = 629665600.

The previous prime is 645407239. The next prime is 645407291. The reversal of 645407281 is 182704546.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 258695056 + 386712225 = 16084^2 + 19665^2 .

It is a cyclic number.

It is not a de Polignac number, because 645407281 - 2²⁹ = 108536369 is a prime.

It is a super-2 number, since 2×645407281² = 833101116735625922, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 645407281.

It is not an unprimeable number, because it can be changed into a prime (645407221) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7870780 + ... + 7870861.

It is an arithmetic number, because the mean of its divisors is an integer number (165287241).

Almost surely, 2^645407281 is an apocalyptic number.

It is an amenable number.

645407281 is a deficient number, since it is larger than the sum of its proper divisors (15741683).

645407281 is a wasteful number, since it uses less digits than its factorization.

645407281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15741682.

The product of its (nonzero) digits is 53760, while the sum is 37.

The square root of 645407281 is about 25404.8672698757. The cubic root of 645407281 is about 864.1940797896.

The spelling of 645407281 in words is "six hundred forty-five million, four hundred seven thousand, two hundred eighty-one".