21123647 has 4 divisors (see below), whose sum is σ = 21216120. Its totient is φ = 21031176.

The previous prime is 21123643. The next prime is 21123653. The reversal of 21123647 is 74632112.

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 21123647 - 2² = 21123643 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 (21123643) 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, 45893 + ... + 46350.

It is an arithmetic number, because the mean of its divisors is an integer number (5304030).

Almost surely, 2^21123647 is an apocalyptic number.

21123647 is a deficient number, since it is larger than the sum of its proper divisors (92473).

21123647 is an equidigital number, since it uses as much as digits as its factorization.

21123647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 92472.

The product of its digits is 2016, while the sum is 26.

The square root of 21123647 is about 4596.0468883596. The cubic root of 21123647 is about 276.4328388362.

Adding to 21123647 its reverse (74632112), we get a palindrome (95755759).

The spelling of 21123647 in words is "twenty-one million, one hundred twenty-three thousand, six hundred forty-seven".