21224681 has 4 divisors (see below), whose sum is σ = 21251664. Its totient is φ = 21197700.

The previous prime is 21224659. The next prime is 21224689. The reversal of 21224681 is 18642212.

It is a happy number.

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 21224681 - 2⁶ = 21224617 is a prime.

It is a super-3 number, since 3×21224681³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21224681.

It is not an unprimeable number, because it can be changed into a prime (21224689) 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, 12275 + ... + 13896.

It is an arithmetic number, because the mean of its divisors is an integer number (5312916).

Almost surely, 2^21224681 is an apocalyptic number.

It is an amenable number.

21224681 is a deficient number, since it is larger than the sum of its proper divisors (26983).

21224681 is an equidigital number, since it uses as much as digits as its factorization.

21224681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26982.

The product of its digits is 1536, while the sum is 26.

The square root of 21224681 is about 4607.0251790065. The cubic root of 21224681 is about 276.8728623675.

Adding to 21224681 its reverse (18642212), we get a palindrome (39866893).

The spelling of 21224681 in words is "twenty-one million, two hundred twenty-four thousand, six hundred eighty-one".