21109985 has 16 divisors (see below), whose sum is σ = 27632640. Its totient is φ = 15387840.

The previous prime is 21109973. The next prime is 21109987. The reversal of 21109985 is 58990112.

It is not a de Polignac number, because 21109985 - 2¹⁴ = 21093601 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21109987) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3080 + ... + 7190.

It is an arithmetic number, because the mean of its divisors is an integer number (1727040).

Almost surely, 2^21109985 is an apocalyptic number.

It is an amenable number.

21109985 is a deficient number, since it is larger than the sum of its proper divisors (6522655).

21109985 is a wasteful number, since it uses less digits than its factorization.

21109985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4208.

The product of its (nonzero) digits is 6480, while the sum is 35.

The square root of 21109985 is about 4594.5603706992. The cubic root of 21109985 is about 276.3732304436.

The spelling of 21109985 in words is "twenty-one million, one hundred nine thousand, nine hundred eighty-five".