21252155 has 4 divisors (see below), whose sum is σ = 25502592. Its totient is φ = 17001720.

The previous prime is 21252151. The next prime is 21252167. The reversal of 21252155 is 55125212.

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

It is not a de Polignac number, because 21252155 - 2² = 21252151 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21252155.

It is not an unprimeable number, because it can be changed into a prime (21252151) 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, 2125211 + ... + 2125220.

It is an arithmetic number, because the mean of its divisors is an integer number (6375648).

Almost surely, 2^21252155 is an apocalyptic number.

21252155 is a deficient number, since it is larger than the sum of its proper divisors (4250437).

21252155 is an equidigital number, since it uses as much as digits as its factorization.

21252155 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4250436.

The product of its digits is 1000, while the sum is 23.

The square root of 21252155 is about 4610.0059652890. The cubic root of 21252155 is about 276.9922756299.

Adding to 21252155 its reverse (55125212), we get a palindrome (76377367).

The spelling of 21252155 in words is "twenty-one million, two hundred fifty-two thousand, one hundred fifty-five".