21387389 has 2 divisors, whose sum is σ = 21387390. Its totient is φ = 21387388.

The previous prime is 21387361. The next prime is 21387391. The reversal of 21387389 is 98378312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17935225 + 3452164 = 4235^2 + 1858^2 .

It is a cyclic number.

It is not a de Polignac number, because 21387389 - 2²⁴ = 4610173 is a prime.

Together with 21387391, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21387319) 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, 10693694 + 10693695.

It is an arithmetic number, because the mean of its divisors is an integer number (10693695).

Almost surely, 2^21387389 is an apocalyptic number.

It is an amenable number.

21387389 is a deficient number, since it is larger than the sum of its proper divisors (1).

21387389 is an equidigital number, since it uses as much as digits as its factorization.

21387389 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 72576, while the sum is 41.

The square root of 21387389 is about 4624.6501489302. The cubic root of 21387389 is about 277.5785628276.

The spelling of 21387389 in words is "twenty-one million, three hundred eighty-seven thousand, three hundred eighty-nine".