21335681 has 4 divisors (see below), whose sum is σ = 21654192. Its totient is φ = 21017172.

The previous prime is 21335647. The next prime is 21335683. The reversal of 21335681 is 18653312.

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 21335681 - 2⁶ = 21335617 is a prime.

It is a super-2 number, since 2×21335681² = 910422567467522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21335683) 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, 159155 + ... + 159288.

It is an arithmetic number, because the mean of its divisors is an integer number (5413548).

Almost surely, 2^21335681 is an apocalyptic number.

It is an amenable number.

21335681 is a deficient number, since it is larger than the sum of its proper divisors (318511).

21335681 is an equidigital number, since it uses as much as digits as its factorization.

21335681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 318510.

The product of its digits is 4320, while the sum is 29.

The square root of 21335681 is about 4619.0562888971. The cubic root of 21335681 is about 277.3546829993.

Adding to 21335681 its reverse (18653312), we get a palindrome (39988993).

The spelling of 21335681 in words is "twenty-one million, three hundred thirty-five thousand, six hundred eighty-one".