21135823 has 2 divisors, whose sum is σ = 21135824. Its totient is φ = 21135822.

The previous prime is 21135797. The next prime is 21135839. The reversal of 21135823 is 32853112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21135823 - 2⁵ = 21135791 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21135223) 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, 10567911 + 10567912.

It is an arithmetic number, because the mean of its divisors is an integer number (10567912).

Almost surely, 2^21135823 is an apocalyptic number.

21135823 is a deficient number, since it is larger than the sum of its proper divisors (1).

21135823 is an equidigital number, since it uses as much as digits as its factorization.

21135823 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1440, while the sum is 25.

The square root of 21135823 is about 4597.3713141316. The cubic root of 21135823 is about 276.4859420360.

Adding to 21135823 its reverse (32853112), we get a palindrome (53988935).

It can be divided in two parts, 2 and 1135823, that multiplied together give a triangular number (2271646 = T₂₁₃₁).

The spelling of 21135823 in words is "twenty-one million, one hundred thirty-five thousand, eight hundred twenty-three".