21123899 has 2 divisors, whose sum is σ = 21123900. Its totient is φ = 21123898.

The previous prime is 21123887. The next prime is 21123901. The reversal of 21123899 is 99832112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21123899 - 2⁸ = 21123643 is a prime.

Together with 21123901, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21123859) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561949 + 10561950.

It is an arithmetic number, because the mean of its divisors is an integer number (10561950).

Almost surely, 2^21123899 is an apocalyptic number.

21123899 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123899 is an equidigital number, since it uses as much as digits as its factorization.

21123899 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7776, while the sum is 35.

The square root of 21123899 is about 4596.0743031418. The cubic root of 21123899 is about 276.4339380908.

It can be divided in two parts, 21123 and 899, that added together give a palindrome (22022).

The spelling of 21123899 in words is "twenty-one million, one hundred twenty-three thousand, eight hundred ninety-nine".