21311320 has 16 divisors (see below), whose sum is σ = 47950560. Its totient is φ = 8524512.

The previous prime is 21311261. The next prime is 21311347. The reversal of 21311320 is 2311312.

It is a self number, because there is not a number n which added to its sum of digits gives 21311320.

It is a congruent 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, 266352 + ... + 266431.

It is an arithmetic number, because the mean of its divisors is an integer number (2996910).

Almost surely, 2^21311320 is an apocalyptic number.

21311320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21311320 is an abundant number, since it is smaller than the sum of its proper divisors (26639240).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21311320 is a wasteful number, since it uses less digits than its factorization.

21311320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 532794 (or 532790 counting only the distinct ones).

The product of its (nonzero) digits is 36, while the sum is 13.

The square root of 21311320 is about 4616.4185252206. The cubic root of 21311320 is about 277.2490819542.

Adding to 21311320 its reverse (2311312), we get a palindrome (23622632).

The spelling of 21311320 in words is "twenty-one million, three hundred eleven thousand, three hundred twenty".