21331681 has 8 divisors (see below), whose sum is σ = 24431040. Its totient is φ = 18245328.

The previous prime is 21331679. The next prime is 21331693. The reversal of 21331681 is 18613312.

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 21331681 - 2¹ = 21331679 is a prime.

It is a super-2 number, since 2×21331681² = 910081228571522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21331621) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 570 + ... + 6556.

It is an arithmetic number, because the mean of its divisors is an integer number (3053880).

Almost surely, 2^21331681 is an apocalyptic number.

It is an amenable number.

21331681 is a deficient number, since it is larger than the sum of its proper divisors (3099359).

21331681 is an equidigital number, since it uses as much as digits as its factorization.

21331681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6503.

The product of its digits is 864, while the sum is 25.

The square root of 21331681 is about 4618.6232797231. The cubic root of 21331681 is about 277.3373491557.

Adding to 21331681 its reverse (18613312), we get a palindrome (39944993).

The spelling of 21331681 in words is "twenty-one million, three hundred thirty-one thousand, six hundred eighty-one".