21369981 has 4 divisors (see below), whose sum is σ = 28493312. Its totient is φ = 14246652.

The previous prime is 21369949. The next prime is 21369989. The reversal of 21369981 is 18996312.

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 21369981 - 2⁵ = 21369949 is a prime.

It is a super-2 number, since 2×21369981² = 913352175880722, 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 (21369989) 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, 3561661 + ... + 3561666.

It is an arithmetic number, because the mean of its divisors is an integer number (7123328).

Almost surely, 2^21369981 is an apocalyptic number.

It is an amenable number.

21369981 is a deficient number, since it is larger than the sum of its proper divisors (7123331).

21369981 is an equidigital number, since it uses as much as digits as its factorization.

21369981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7123330.

The product of its digits is 23328, while the sum is 39.

The square root of 21369981 is about 4622.7676774850. The cubic root of 21369981 is about 277.5032318429.

The spelling of 21369981 in words is "twenty-one million, three hundred sixty-nine thousand, nine hundred eighty-one".