21099553 has 4 divisors (see below), whose sum is σ = 21178260. Its totient is φ = 21020848.

The previous prime is 21099539. The next prime is 21099563. The reversal of 21099553 is 35599012.

It is a happy number.

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 2712609 + 18386944 = 1647^2 + 4288^2 .

It is a cyclic number.

It is not a de Polignac number, because 21099553 - 2⁹ = 21099041 is a prime.

It is a super-2 number, since 2×21099553² = 890382273599618, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21099503) 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, 38950 + ... + 39487.

It is an arithmetic number, because the mean of its divisors is an integer number (5294565).

Almost surely, 2^21099553 is an apocalyptic number.

It is an amenable number.

21099553 is a deficient number, since it is larger than the sum of its proper divisors (78707).

21099553 is an equidigital number, since it uses as much as digits as its factorization.

21099553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 78706.

The product of its (nonzero) digits is 12150, while the sum is 34.

The square root of 21099553 is about 4593.4249748962. The cubic root of 21099553 is about 276.3276974791.

The spelling of 21099553 in words is "twenty-one million, ninety-nine thousand, five hundred fifty-three".