21097553 has 4 divisors (see below), whose sum is σ = 21106800. Its totient is φ = 21088308.

The previous prime is 21097547. The next prime is 21097567. The reversal of 21097553 is 35579012.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21097553 - 2¹⁴ = 21081169 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21097513) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1526 + ... + 6672.

It is an arithmetic number, because the mean of its divisors is an integer number (5276700).

Almost surely, 2^21097553 is an apocalyptic number.

It is an amenable number.

21097553 is a deficient number, since it is larger than the sum of its proper divisors (9247).

21097553 is an equidigital number, since it uses as much as digits as its factorization.

21097553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9246.

The product of its (nonzero) digits is 9450, while the sum is 32.

The square root of 21097553 is about 4593.2072672589. The cubic root of 21097553 is about 276.3189662853.

The spelling of 21097553 in words is "twenty-one million, ninety-seven thousand, five hundred fifty-three".