21123381 has 4 divisors (see below), whose sum is σ = 28164512. Its totient is φ = 14082252.

The previous prime is 21123373. The next prime is 21123391. The reversal of 21123381 is 18332112.

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 21123381 - 2³ = 21123373 is a prime.

It is a super-2 number, since 2×21123381² = 892394449742322, 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 (21123301) 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, 3520561 + ... + 3520566.

It is an arithmetic number, because the mean of its divisors is an integer number (7041128).

Almost surely, 2^21123381 is an apocalyptic number.

It is an amenable number.

21123381 is a deficient number, since it is larger than the sum of its proper divisors (7041131).

21123381 is an equidigital number, since it uses as much as digits as its factorization.

21123381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7041130.

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

The square root of 21123381 is about 4596.0179503566. The cubic root of 21123381 is about 276.4316785024.

Adding to 21123381 its reverse (18332112), we get a palindrome (39455493).

The spelling of 21123381 in words is "twenty-one million, one hundred twenty-three thousand, three hundred eighty-one".