21621155 has 4 divisors (see below), whose sum is σ = 25945392. Its totient is φ = 17296920.

The previous prime is 21621143. The next prime is 21621179. The reversal of 21621155 is 55112612.

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 21621155 - 2⁴ = 21621139 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 21621155.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2162111 + ... + 2162120.

It is an arithmetic number, because the mean of its divisors is an integer number (6486348).

Almost surely, 2^21621155 is an apocalyptic number.

21621155 is a deficient number, since it is larger than the sum of its proper divisors (4324237).

21621155 is an equidigital number, since it uses as much as digits as its factorization.

21621155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4324236.

The product of its digits is 600, while the sum is 23.

The square root of 21621155 is about 4649.8553740950. The cubic root of 21621155 is about 278.5862196210.

Adding to 21621155 its reverse (55112612), we get a palindrome (76733767).

The spelling of 21621155 in words is "twenty-one million, six hundred twenty-one thousand, one hundred fifty-five".