21231381 has 4 divisors (see below), whose sum is σ = 28308512. Its totient is φ = 14154252.

The previous prime is 21231359. The next prime is 21231389. The reversal of 21231381 is 18313212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21231381 - 2⁷ = 21231253 is a prime.

It is a super-2 number, since 2×21231381² = 901543078334322, 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 (21231389) 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, 3538561 + ... + 3538566.

It is an arithmetic number, because the mean of its divisors is an integer number (7077128).

Almost surely, 2^21231381 is an apocalyptic number.

It is an amenable number.

21231381 is a deficient number, since it is larger than the sum of its proper divisors (7077131).

21231381 is an equidigital number, since it uses as much as digits as its factorization.

21231381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7077130.

The product of its digits is 288, while the sum is 21.

The square root of 21231381 is about 4607.7522719869. The cubic root of 21231381 is about 276.9019928095.

Adding to 21231381 its reverse (18313212), we get a palindrome (39544593).

It can be divided in two parts, 21231 and 381, that added together give a palindrome (21612).

The spelling of 21231381 in words is "twenty-one million, two hundred thirty-one thousand, three hundred eighty-one".