21287985 has 8 divisors (see below), whose sum is σ = 34060800. Its totient is φ = 11353584.

The previous prime is 21287951. The next prime is 21287993. The reversal of 21287985 is 58978212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21287985 - 2⁶ = 21287921 is a prime.

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 709585 + ... + 709614.

It is an arithmetic number, because the mean of its divisors is an integer number (4257600).

Almost surely, 2^21287985 is an apocalyptic number.

It is an amenable number.

21287985 is a deficient number, since it is larger than the sum of its proper divisors (12772815).

21287985 is a wasteful number, since it uses less digits than its factorization.

21287985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1419207.

The product of its digits is 80640, while the sum is 42.

The square root of 21287985 is about 4613.8904408319. The cubic root of 21287985 is about 277.1478529660.

The spelling of 21287985 in words is "twenty-one million, two hundred eighty-seven thousand, nine hundred eighty-five".