21006187 has 4 divisors (see below), whose sum is σ = 21123720. Its totient is φ = 20888656.

The previous prime is 21006163. The next prime is 21006217. The reversal of 21006187 is 78160012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21006187 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21006137) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 58498 + ... + 58855.

It is an arithmetic number, because the mean of its divisors is an integer number (5280930).

Almost surely, 2^21006187 is an apocalyptic number.

21006187 is a deficient number, since it is larger than the sum of its proper divisors (117533).

21006187 is a wasteful number, since it uses less digits than its factorization.

21006187 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 117532.

The product of its (nonzero) digits is 672, while the sum is 25.

The square root of 21006187 is about 4583.2507022854. The cubic root of 21006187 is about 275.9195093648.

Adding to 21006187 its reverse (78160012), we get a palindrome (99166199).

The spelling of 21006187 in words is "twenty-one million, six thousand, one hundred eighty-seven".