21138647 has 4 divisors (see below), whose sum is σ = 21256920. Its totient is φ = 21020376.

The previous prime is 21138619. The next prime is 21138713. The reversal of 21138647 is 74683112.

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

It is a cyclic number.

It is not a de Polignac number, because 21138647 - 2²⁰ = 20090071 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21138547) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 58868 + ... + 59225.

It is an arithmetic number, because the mean of its divisors is an integer number (5314230).

Almost surely, 2^21138647 is an apocalyptic number.

21138647 is a deficient number, since it is larger than the sum of its proper divisors (118273).

21138647 is a wasteful number, since it uses less digits than its factorization.

21138647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 118272.

The product of its digits is 8064, while the sum is 32.

The square root of 21138647 is about 4597.6784359065. The cubic root of 21138647 is about 276.4982554360.

The spelling of 21138647 in words is "twenty-one million, one hundred thirty-eight thousand, six hundred forty-seven".