647681 has 4 divisors (see below), whose sum is σ = 651264. Its totient is φ = 644100.

The previous prime is 647663. The next prime is 647687. The reversal of 647681 is 186746.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 647681 - 2⁶ = 647617 is a prime.

It is a super-2 number, since 2×647681² = 838981355522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 647681.

It is not an unprimeable number, because it can be changed into a prime (647687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1505 + ... + 1886.

It is an arithmetic number, because the mean of its divisors is an integer number (162816).

2⁶⁴⁷⁶⁸¹ is an apocalyptic number.

It is an amenable number.

647681 is a deficient number, since it is larger than the sum of its proper divisors (3583).

647681 is a wasteful number, since it uses less digits than its factorization.

647681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3582.

The product of its digits is 8064, while the sum is 32.

The square root of 647681 is about 804.7863070406. The cubic root of 647681 is about 86.5207719614.

The spelling of 647681 in words is "six hundred forty-seven thousand, six hundred eighty-one".