21306553 has 8 divisors (see below), whose sum is σ = 21614400. Its totient is φ = 21001200.

The previous prime is 21306547. The next prime is 21306587. The reversal of 21306553 is 35560312.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21306553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21306953) 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, 22026 + ... + 22972.

It is an arithmetic number, because the mean of its divisors is an integer number (2701800).

Almost surely, 2^21306553 is an apocalyptic number.

It is an amenable number.

21306553 is a deficient number, since it is larger than the sum of its proper divisors (307847).

21306553 is a wasteful number, since it uses less digits than its factorization.

21306553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1247.

The product of its (nonzero) digits is 2700, while the sum is 25.

The square root of 21306553 is about 4615.9021870053. The cubic root of 21306553 is about 277.2284083571.

Adding to 21306553 its reverse (35560312), we get a palindrome (56866865).

The spelling of 21306553 in words is "twenty-one million, three hundred six thousand, five hundred fifty-three".