21331381 has 4 divisors (see below), whose sum is σ = 21342700. Its totient is φ = 21320064.

The previous prime is 21331369. The next prime is 21331399. The reversal of 21331381 is 18313312.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 2452356 + 18879025 = 1566^2 + 4345^2 .

It is a cyclic number.

It is not a de Polignac number, because 21331381 - 2¹³ = 21323189 is a prime.

It is a super-2 number, since 2×21331381² = 910055630734322, 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 (21331361) 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, 2076 + ... + 6853.

It is an arithmetic number, because the mean of its divisors is an integer number (5335675).

Almost surely, 2^21331381 is an apocalyptic number.

It is an amenable number.

21331381 is a deficient number, since it is larger than the sum of its proper divisors (11319).

21331381 is an equidigital number, since it uses as much as digits as its factorization.

21331381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11318.

The product of its digits is 432, while the sum is 22.

The square root of 21331381 is about 4618.5908023985. The cubic root of 21331381 is about 277.3360490301.

Adding to 21331381 its reverse (18313312), we get a palindrome (39644693).

It can be divided in two parts, 21331 and 381, that added together give a palindrome (21712).

The spelling of 21331381 in words is "twenty-one million, three hundred thirty-one thousand, three hundred eighty-one".