21185389 has 2 divisors, whose sum is σ = 21185390. Its totient is φ = 21185388.

The previous prime is 21185387. The next prime is 21185393. The reversal of 21185389 is 98358112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17015625 + 4169764 = 4125^2 + 2042^2 .

It is a cyclic number.

It is not a de Polignac number, because 21185389 - 2¹ = 21185387 is a prime.

Together with 21185387, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21185387) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10592694 + 10592695.

It is an arithmetic number, because the mean of its divisors is an integer number (10592695).

Almost surely, 2^21185389 is an apocalyptic number.

It is an amenable number.

21185389 is a deficient number, since it is larger than the sum of its proper divisors (1).

21185389 is an equidigital number, since it uses as much as digits as its factorization.

21185389 is an evil number, because the sum of its binary digits is even.

The product of its digits is 17280, while the sum is 37.

The square root of 21185389 is about 4602.7588466049. The cubic root of 21185389 is about 276.7019040294.

The spelling of 21185389 in words is "twenty-one million, one hundred eighty-five thousand, three hundred eighty-nine".