21020311 has 4 divisors (see below), whose sum is σ = 22637272. Its totient is φ = 19403352.

The previous prime is 21020303. The next prime is 21020339. The reversal of 21020311 is 11302012.

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 21020311 - 2³ = 21020303 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 (21020011) 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, 808461 + ... + 808486.

It is an arithmetic number, because the mean of its divisors is an integer number (5659318).

Almost surely, 2^21020311 is an apocalyptic number.

21020311 is a deficient number, since it is larger than the sum of its proper divisors (1616961).

21020311 is a wasteful number, since it uses less digits than its factorization.

21020311 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1616960.

The product of its (nonzero) digits is 12, while the sum is 10.

The square root of 21020311 is about 4584.7912711486. The cubic root of 21020311 is about 275.9813358169.

Adding to 21020311 its reverse (11302012), we get a palindrome (32322323).

The spelling of 21020311 in words is "twenty-one million, twenty thousand, three hundred eleven".