21185155 has 4 divisors (see below), whose sum is σ = 25422192. Its totient is φ = 16948120.

The previous prime is 21185123. The next prime is 21185173. The reversal of 21185155 is 55158112.

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

It is not a de Polignac number, because 21185155 - 2⁵ = 21185123 is a prime.

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, 2118511 + ... + 2118520.

It is an arithmetic number, because the mean of its divisors is an integer number (6355548).

Almost surely, 2^21185155 is an apocalyptic number.

21185155 is a deficient number, since it is larger than the sum of its proper divisors (4237037).

21185155 is an equidigital number, since it uses as much as digits as its factorization.

21185155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4237036.

The product of its digits is 2000, while the sum is 28.

The square root of 21185155 is about 4602.7334269975. The cubic root of 21185155 is about 276.7008852694.

The spelling of 21185155 in words is "twenty-one million, one hundred eighty-five thousand, one hundred fifty-five".