21155311 has 4 divisors (see below), whose sum is σ = 21605472. Its totient is φ = 20705152.

The previous prime is 21155287. The next prime is 21155339. The reversal of 21155311 is 11355112.

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 21155311 - 2⁹ = 21154799 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21155371) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 225010 + ... + 225103.

It is an arithmetic number, because the mean of its divisors is an integer number (5401368).

Almost surely, 2^21155311 is an apocalyptic number.

21155311 is a deficient number, since it is larger than the sum of its proper divisors (450161).

21155311 is an equidigital number, since it uses as much as digits as its factorization.

21155311 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 450160.

The product of its digits is 150, while the sum is 19.

The square root of 21155311 is about 4599.4902978482. The cubic root of 21155311 is about 276.5708926411.

The spelling of 21155311 in words is "twenty-one million, one hundred fifty-five thousand, three hundred eleven".