21381389 has 2 divisors, whose sum is σ = 21381390. Its totient is φ = 21381388.

The previous prime is 21381383. The next prime is 21381407. The reversal of 21381389 is 98318312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13213225 + 8168164 = 3635^2 + 2858^2 .

It is a cyclic number.

It is not a de Polignac number, because 21381389 - 2⁸ = 21381133 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21381383) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10690694 + 10690695.

It is an arithmetic number, because the mean of its divisors is an integer number (10690695).

Almost surely, 2^21381389 is an apocalyptic number.

It is an amenable number.

21381389 is a deficient number, since it is larger than the sum of its proper divisors (1).

21381389 is an equidigital number, since it uses as much as digits as its factorization.

21381389 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10368, while the sum is 35.

The square root of 21381389 is about 4624.0014057091. The cubic root of 21381389 is about 277.5526031816.

The spelling of 21381389 in words is "twenty-one million, three hundred eighty-one thousand, three hundred eighty-nine".