21006985 has 8 divisors (see below), whose sum is σ = 26691336. Its totient is φ = 15816960.

The previous prime is 21006977. The next prime is 21007001. The reversal of 21006985 is 58960012.

It can be written as a sum of positive squares in 4 ways, for example, as 10169721 + 10837264 = 3189^2 + 3292^2 .

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

It is not a de Polignac number, because 21006985 - 2³ = 21006977 is a prime.

It is a Duffinian 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, 123486 + ... + 123655.

It is an arithmetic number, because the mean of its divisors is an integer number (3336417).

Almost surely, 2^21006985 is an apocalyptic number.

It is an amenable number.

21006985 is a deficient number, since it is larger than the sum of its proper divisors (5684351).

21006985 is a wasteful number, since it uses less digits than its factorization.

21006985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 247163.

The product of its (nonzero) digits is 4320, while the sum is 31.

The square root of 21006985 is about 4583.3377575736. The cubic root of 21006985 is about 275.9230032716.

Adding to 21006985 its reverse (58960012), we get a palindrome (79966997).

The spelling of 21006985 in words is "twenty-one million, six thousand, nine hundred eighty-five".