21864239 has 2 divisors, whose sum is σ = 21864240. Its totient is φ = 21864238.

The previous prime is 21864229. The next prime is 21864263. The reversal of 21864239 is 93246812.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21864239 - 2¹⁶ = 21798703 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21864199 and 21864208.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21864209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932119 + 10932120.

It is an arithmetic number, because the mean of its divisors is an integer number (10932120).

Almost surely, 2^21864239 is an apocalyptic number.

21864239 is a deficient number, since it is larger than the sum of its proper divisors (1).

21864239 is an equidigital number, since it uses as much as digits as its factorization.

21864239 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 35.

The square root of 21864239 is about 4675.9211926635. The cubic root of 21864239 is about 279.6263681442.

The spelling of 21864239 in words is "twenty-one million, eight hundred sixty-four thousand, two hundred thirty-nine".