21138823 has 2 divisors, whose sum is σ = 21138824. Its totient is φ = 21138822.

The previous prime is 21138791. The next prime is 21138847. The reversal of 21138823 is 32883112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21138823 - 2⁵ = 21138791 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21138791 and 21138800.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21138853) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10569411 + 10569412.

It is an arithmetic number, because the mean of its divisors is an integer number (10569412).

Almost surely, 2^21138823 is an apocalyptic number.

21138823 is a deficient number, since it is larger than the sum of its proper divisors (1).

21138823 is an equidigital number, since it uses as much as digits as its factorization.

21138823 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2304, while the sum is 28.

The square root of 21138823 is about 4597.6975759613. The cubic root of 21138823 is about 276.4990228071.

The spelling of 21138823 in words is "twenty-one million, one hundred thirty-eight thousand, eight hundred twenty-three".