21864389 has 2 divisors, whose sum is σ = 21864390. Its totient is φ = 21864388.

The previous prime is 21864377. The next prime is 21864407. The reversal of 21864389 is 98346812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21669025 + 195364 = 4655^2 + 442^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21864389 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21864989) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932194 + 10932195.

It is an arithmetic number, because the mean of its divisors is an integer number (10932195).

Almost surely, 2^21864389 is an apocalyptic number.

It is an amenable number.

21864389 is a deficient number, since it is larger than the sum of its proper divisors (1).

21864389 is an equidigital number, since it uses as much as digits as its factorization.

21864389 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 82944, while the sum is 41.

The square root of 21864389 is about 4675.9372322562. The cubic root of 21864389 is about 279.6270076033.

The spelling of 21864389 in words is "twenty-one million, eight hundred sixty-four thousand, three hundred eighty-nine".