21521155 has 4 divisors (see below), whose sum is σ = 25825392. Its totient is φ = 17216920.

The previous prime is 21521141. The next prime is 21521183. The reversal of 21521155 is 55112512.

It is a happy number.

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

It is not a de Polignac number, because 21521155 - 2²³ = 13132547 is a prime.

It is a super-2 number, since 2×21521155² = 926320225068050, which contains 22 as substring.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian 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, 2152111 + ... + 2152120.

It is an arithmetic number, because the mean of its divisors is an integer number (6456348).

Almost surely, 2^21521155 is an apocalyptic number.

21521155 is a deficient number, since it is larger than the sum of its proper divisors (4304237).

21521155 is an equidigital number, since it uses as much as digits as its factorization.

21521155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4304236.

The product of its digits is 500, while the sum is 22.

The square root of 21521155 is about 4639.0898891916. The cubic root of 21521155 is about 278.1560594022.

Adding to 21521155 its reverse (55112512), we get a palindrome (76633667).

The spelling of 21521155 in words is "twenty-one million, five hundred twenty-one thousand, one hundred fifty-five".