21678681 has 4 divisors (see below), whose sum is σ = 28904912. Its totient is φ = 14452452.

The previous prime is 21678667. The next prime is 21678697. The reversal of 21678681 is 18687612.

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 not a de Polignac number, because 21678681 - 2¹³ = 21670489 is a prime.

It is a super-2 number, since 2×21678681² = 939930419799522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21678611) 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, 3613111 + ... + 3613116.

It is an arithmetic number, because the mean of its divisors is an integer number (7226228).

Almost surely, 2^21678681 is an apocalyptic number.

It is an amenable number.

21678681 is a deficient number, since it is larger than the sum of its proper divisors (7226231).

21678681 is an equidigital number, since it uses as much as digits as its factorization.

21678681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7226230.

The product of its digits is 32256, while the sum is 39.

The square root of 21678681 is about 4656.0370488217. The cubic root of 21678681 is about 278.8330728962.

The spelling of 21678681 in words is "twenty-one million, six hundred seventy-eight thousand, six hundred eighty-one".