21680731 has 8 divisors (see below), whose sum is σ = 22160384. Its totient is φ = 21205800.

The previous prime is 21680717. The next prime is 21680741. The reversal of 21680731 is 13708612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21680731 - 2⁵ = 21680699 is a prime.

It is a super-2 number, since 2×21680731² = 940108193388722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21680731.

It is not an unprimeable number, because it can be changed into a prime (21680741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9046 + ... + 11188.

It is an arithmetic number, because the mean of its divisors is an integer number (2770048).

Almost surely, 2^21680731 is an apocalyptic number.

21680731 is a deficient number, since it is larger than the sum of its proper divisors (479653).

21680731 is a wasteful number, since it uses less digits than its factorization.

21680731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2361.

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 21680731 is about 4656.2571879139. The cubic root of 21680731 is about 278.8418617117.

The spelling of 21680731 in words is "twenty-one million, six hundred eighty thousand, seven hundred thirty-one".