21308389 has 2 divisors, whose sum is σ = 21308390. Its totient is φ = 21308388.

The previous prime is 21308383. The next prime is 21308393. The reversal of 21308389 is 98380312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12723489 + 8584900 = 3567^2 + 2930^2 .

It is a cyclic number.

It is not a de Polignac number, because 21308389 - 2⁹ = 21307877 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21308383) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10654194 + 10654195.

It is an arithmetic number, because the mean of its divisors is an integer number (10654195).

Almost surely, 2^21308389 is an apocalyptic number.

It is an amenable number.

21308389 is a deficient number, since it is larger than the sum of its proper divisors (1).

21308389 is an equidigital number, since it uses as much as digits as its factorization.

21308389 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10368, while the sum is 34.

The square root of 21308389 is about 4616.1010604188. The cubic root of 21308389 is about 277.2363711145.

The spelling of 21308389 in words is "twenty-one million, three hundred eight thousand, three hundred eighty-nine".