21515135 has 4 divisors (see below), whose sum is σ = 25818168. Its totient is φ = 17212104.

The previous prime is 21515113. The next prime is 21515159. The reversal of 21515135 is 53151512.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21515135 - 2¹⁶ = 21449599 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 21515135.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2151509 + ... + 2151518.

It is an arithmetic number, because the mean of its divisors is an integer number (6454542).

Almost surely, 2^21515135 is an apocalyptic number.

21515135 is a deficient number, since it is larger than the sum of its proper divisors (4303033).

21515135 is an equidigital number, since it uses as much as digits as its factorization.

21515135 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4303032.

The product of its digits is 750, while the sum is 23.

The square root of 21515135 is about 4638.4410096497. The cubic root of 21515135 is about 278.1301212708.

Adding to 21515135 its reverse (53151512), we get a palindrome (74666647).

The spelling of 21515135 in words is "twenty-one million, five hundred fifteen thousand, one hundred thirty-five".