21392381 has 2 divisors, whose sum is σ = 21392382. Its totient is φ = 21392380.

The previous prime is 21392359. The next prime is 21392383. The reversal of 21392381 is 18329312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10725625 + 10666756 = 3275^2 + 3266^2 .

It is a cyclic number.

It is not a de Polignac number, because 21392381 - 2⁶ = 21392317 is a prime.

It is a super-2 number, since 2×21392381² = 915267929698322, which contains 22 as substring.

Together with 21392383, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21392383) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10696190 + 10696191.

It is an arithmetic number, because the mean of its divisors is an integer number (10696191).

Almost surely, 2^21392381 is an apocalyptic number.

It is an amenable number.

21392381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21392381 is an equidigital number, since it uses as much as digits as its factorization.

21392381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2592, while the sum is 29.

The square root of 21392381 is about 4625.1898339420. The cubic root of 21392381 is about 277.6001575532.

The spelling of 21392381 in words is "twenty-one million, three hundred ninety-two thousand, three hundred eighty-one".