21166553 has 4 divisors (see below), whose sum is σ = 21738660. Its totient is φ = 20594448.

The previous prime is 21166529. The next prime is 21166559. The reversal of 21166553 is 35566112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 18079504 + 3087049 = 4252^2 + 1757^2 .

It is a cyclic number.

It is not a de Polignac number, because 21166553 - 2⁶ = 21166489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21166559) 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, 285998 + ... + 286071.

It is an arithmetic number, because the mean of its divisors is an integer number (5434665).

Almost surely, 2^21166553 is an apocalyptic number.

It is an amenable number.

21166553 is a deficient number, since it is larger than the sum of its proper divisors (572107).

21166553 is an equidigital number, since it uses as much as digits as its factorization.

21166553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 572106.

The product of its digits is 5400, while the sum is 29.

The square root of 21166553 is about 4600.7122274709. The cubic root of 21166553 is about 276.6198741851.

The spelling of 21166553 in words is "twenty-one million, one hundred sixty-six thousand, five hundred fifty-three".