21331387 has 16 divisors (see below), whose sum is σ = 27101952. Its totient is φ = 16305120.

The previous prime is 21331369. The next prime is 21331399. The reversal of 21331387 is 78313312.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21331387 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21331187) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1468 + ... + 6694.

It is an arithmetic number, because the mean of its divisors is an integer number (1693872).

Almost surely, 2^21331387 is an apocalyptic number.

21331387 is a deficient number, since it is larger than the sum of its proper divisors (5770565).

21331387 is a wasteful number, since it uses less digits than its factorization.

21331387 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5298.

The product of its digits is 3024, while the sum is 28.

The square root of 21331387 is about 4618.5914519472. The cubic root of 21331387 is about 277.3360750327.

Adding to 21331387 its reverse (78313312), we get a palindrome (99644699).

It can be divided in two parts, 2133138 and 7, that added together give a triangular number (2133145 = T₂₀₆₅).

The spelling of 21331387 in words is "twenty-one million, three hundred thirty-one thousand, three hundred eighty-seven".