21078311 has 4 divisors (see below), whose sum is σ = 21271800. Its totient is φ = 20884824.

The previous prime is 21078307. The next prime is 21078319. The reversal of 21078311 is 11387012.

It is a happy number.

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 21078311 - 2² = 21078307 is a prime.

It is a super-2 number, since 2×21078311² = 888590389225442, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21078319) 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, 96581 + ... + 96798.

It is an arithmetic number, because the mean of its divisors is an integer number (5317950).

Almost surely, 2^21078311 is an apocalyptic number.

21078311 is a deficient number, since it is larger than the sum of its proper divisors (193489).

21078311 is a wasteful number, since it uses less digits than its factorization.

21078311 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 193488.

The product of its (nonzero) digits is 336, while the sum is 23.

The square root of 21078311 is about 4591.1121746261. The cubic root of 21078311 is about 276.2349352636.

The spelling of 21078311 in words is "twenty-one million, seventy-eight thousand, three hundred eleven".