21155243 has 4 divisors (see below), whose sum is σ = 21190368. Its totient is φ = 21120120.

The previous prime is 21155219. The next prime is 21155257. The reversal of 21155243 is 34255112.

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 21155243 - 2⁶ = 21155179 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21155263) by changing a digit.

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, 16643 + ... + 17868.

It is an arithmetic number, because the mean of its divisors is an integer number (5297592).

Almost surely, 2^21155243 is an apocalyptic number.

21155243 is a deficient number, since it is larger than the sum of its proper divisors (35125).

21155243 is an equidigital number, since it uses as much as digits as its factorization.

21155243 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35124.

The product of its digits is 1200, while the sum is 23.

The square root of 21155243 is about 4599.4829057189. The cubic root of 21155243 is about 276.5705963114.

The spelling of 21155243 in words is "twenty-one million, one hundred fifty-five thousand, two hundred forty-three".