640082781 has 12 divisors (see below), whose sum is σ = 995684508. Its totient is φ = 393897024.

The previous prime is 640082741. The next prime is 640082791. The reversal of 640082781 is 187280046.

640082781 is a `hidden beast` number, since 640 + 0 + 8 + 2 + 7 + 8 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 189200025 + 450882756 = 13755^2 + 21234^2 .

It is not a de Polignac number, because 640082781 - 2⁶ = 640082717 is a prime.

It is a super-2 number, since 2×640082781² = 819411933065387922, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640082701) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2735280 + ... + 2735513.

It is an arithmetic number, because the mean of its divisors is an integer number (82973709).

Almost surely, 2^640082781 is an apocalyptic number.

It is an amenable number.

640082781 is a deficient number, since it is larger than the sum of its proper divisors (355601727).

640082781 is a wasteful number, since it uses less digits than its factorization.

640082781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5470812 (or 5470809 counting only the distinct ones).

The product of its (nonzero) digits is 21504, while the sum is 36.

The square root of 640082781 is about 25299.8573316136. The cubic root of 640082781 is about 861.8110298813.

The spelling of 640082781 in words is "six hundred forty million, eighty-two thousand, seven hundred eighty-one".