21539985 has 16 divisors (see below), whose sum is σ = 34558080. Its totient is φ = 11456640.

The previous prime is 21539971. The next prime is 21539993. The reversal of 21539985 is 58993512.

It is not a de Polignac number, because 21539985 - 2⁸ = 21539729 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4380 + ... + 7890.

It is an arithmetic number, because the mean of its divisors is an integer number (2159880).

Almost surely, 2^21539985 is an apocalyptic number.

It is an amenable number.

21539985 is a deficient number, since it is larger than the sum of its proper divisors (13018095).

21539985 is a wasteful number, since it uses less digits than its factorization.

21539985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3928.

The product of its digits is 97200, while the sum is 42.

The square root of 21539985 is about 4641.1189383596. The cubic root of 21539985 is about 278.2371602503.

The spelling of 21539985 in words is "twenty-one million, five hundred thirty-nine thousand, nine hundred eighty-five".