21388189 has 2 divisors, whose sum is σ = 21388190. Its totient is φ = 21388188.

The previous prime is 21388181. The next prime is 21388201. The reversal of 21388189 is 98188312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13935289 + 7452900 = 3733^2 + 2730^2 .

It is a cyclic number.

It is not a de Polignac number, because 21388189 - 2³ = 21388181 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21388181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10694094 + 10694095.

It is an arithmetic number, because the mean of its divisors is an integer number (10694095).

Almost surely, 2^21388189 is an apocalyptic number.

It is an amenable number.

21388189 is a deficient number, since it is larger than the sum of its proper divisors (1).

21388189 is an equidigital number, since it uses as much as digits as its factorization.

21388189 is an evil number, because the sum of its binary digits is even.

The product of its digits is 27648, while the sum is 40.

The square root of 21388189 is about 4624.7366411505. The cubic root of 21388189 is about 277.5820237469.

The spelling of 21388189 in words is "twenty-one million, three hundred eighty-eight thousand, one hundred eighty-nine".