21308647 has 4 divisors (see below), whose sum is σ = 21548160. Its totient is φ = 21069136.

The previous prime is 21308629. The next prime is 21308653. The reversal of 21308647 is 74680312.

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-21308647 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 (21308047) 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, 119623 + ... + 119800.

It is an arithmetic number, because the mean of its divisors is an integer number (5387040).

Almost surely, 2^21308647 is an apocalyptic number.

21308647 is a deficient number, since it is larger than the sum of its proper divisors (239513).

21308647 is an equidigital number, since it uses as much as digits as its factorization.

21308647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 239512.

The product of its (nonzero) digits is 8064, while the sum is 31.

The square root of 21308647 is about 4616.1290059963. The cubic root of 21308647 is about 277.2374900274.

Adding to 21308647 its reverse (74680312), we get a palindrome (95988959).

The spelling of 21308647 in words is "twenty-one million, three hundred eight thousand, six hundred forty-seven".