21155597 has 4 divisors (see below), whose sum is σ = 21166716. Its totient is φ = 21144480.

The previous prime is 21155591. The next prime is 21155611. The reversal of 21155597 is 79555112.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 18826921 + 2328676 = 4339^2 + 1526^2 .

It is a cyclic number.

It is not a de Polignac number, because 21155597 - 2¹⁴ = 21139213 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21155591) 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, 1904 + ... + 6777.

It is an arithmetic number, because the mean of its divisors is an integer number (5291679).

Almost surely, 2^21155597 is an apocalyptic number.

It is an amenable number.

21155597 is a deficient number, since it is larger than the sum of its proper divisors (11119).

21155597 is an equidigital number, since it uses as much as digits as its factorization.

21155597 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11118.

The product of its digits is 15750, while the sum is 35.

The square root of 21155597 is about 4599.5213881446. The cubic root of 21155597 is about 276.5721389620.

The spelling of 21155597 in words is "twenty-one million, one hundred fifty-five thousand, five hundred ninety-seven".