21389999 has 2 divisors, whose sum is σ = 21390000. Its totient is φ = 21389998.

The previous prime is 21389971. The next prime is 21390007. The reversal of 21389999 is 99998312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21389999 - 2⁸ = 21389743 is a prime.

21389999 is a modest number, since divided by 9999 gives 2138 as remainder.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21389909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10694999 + 10695000.

It is an arithmetic number, because the mean of its divisors is an integer number (10695000).

Almost surely, 2^21389999 is an apocalyptic number.

21389999 is a deficient number, since it is larger than the sum of its proper divisors (1).

21389999 is an equidigital number, since it uses as much as digits as its factorization.

21389999 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 314928, while the sum is 50.

The square root of 21389999 is about 4624.9323238292. The cubic root of 21389999 is about 277.5898537583.

The spelling of 21389999 in words is "twenty-one million, three hundred eighty-nine thousand, nine hundred ninety-nine".