21389903 has 2 divisors, whose sum is σ = 21389904. Its totient is φ = 21389902.

The previous prime is 21389891. The next prime is 21389909. The reversal of 21389903 is 30998312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21389903 - 2⁴ = 21389887 is a prime.

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 polite number, since it can be written as a sum of consecutive naturals, namely, 10694951 + 10694952.

It is an arithmetic number, because the mean of its divisors is an integer number (10694952).

Almost surely, 2^21389903 is an apocalyptic number.

21389903 is a deficient number, since it is larger than the sum of its proper divisors (1).

21389903 is an equidigital number, since it uses as much as digits as its factorization.

21389903 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11664, while the sum is 35.

The square root of 21389903 is about 4624.9219452873. The cubic root of 21389903 is about 277.5894384760.

The spelling of 21389903 in words is "twenty-one million, three hundred eighty-nine thousand, nine hundred three".