21808553 has 8 divisors (see below), whose sum is σ = 23624328. Its totient is φ = 20012544.

The previous prime is 21808547. The next prime is 21808559. The reversal of 21808553 is 35580812.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21808547) and next prime (21808559).

It can be written as a sum of positive squares in 4 ways, for example, as 1087849 + 20720704 = 1043^2 + 4552^2 .

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 21808553 - 2⁶ = 21808489 is a prime.

It is a super-2 number, since 2×21808553² = 951225967907618, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21808559) 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, 2600 + ... + 7097.

It is an arithmetic number, because the mean of its divisors is an integer number (2953041).

Almost surely, 2^21808553 is an apocalyptic number.

It is an amenable number.

21808553 is a deficient number, since it is larger than the sum of its proper divisors (1815775).

21808553 is a wasteful number, since it uses less digits than its factorization.

21808553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9883.

The product of its (nonzero) digits is 9600, while the sum is 32.

The square root of 21808553 is about 4669.9628478180. The cubic root of 21808553 is about 279.3887729832.

The spelling of 21808553 in words is "twenty-one million, eight hundred eight thousand, five hundred fifty-three".