21816553 has 4 divisors (see below), whose sum is σ = 23799888. Its totient is φ = 19833220.

The previous prime is 21816547. The next prime is 21816577. The reversal of 21816553 is 35561812.

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 not a de Polignac number, because 21816553 - 2¹³ = 21808361 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21816583) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 991651 + ... + 991672.

It is an arithmetic number, because the mean of its divisors is an integer number (5949972).

Almost surely, 2^21816553 is an apocalyptic number.

It is an amenable number.

21816553 is a deficient number, since it is larger than the sum of its proper divisors (1983335).

21816553 is a wasteful number, since it uses less digits than its factorization.

21816553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1983334.

The product of its digits is 7200, while the sum is 31.

The square root of 21816553 is about 4670.8193071452. The cubic root of 21816553 is about 279.4229314001.

The spelling of 21816553 in words is "twenty-one million, eight hundred sixteen thousand, five hundred fifty-three".