21279647 has 4 divisors (see below), whose sum is σ = 21328560. Its totient is φ = 21230736.

The previous prime is 21279637. The next prime is 21279653. The reversal of 21279647 is 74697212.

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 21279647 - 2¹⁶ = 21214111 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21279647.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21279637) 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, 23798 + ... + 24675.

It is an arithmetic number, because the mean of its divisors is an integer number (5332140).

Almost surely, 2^21279647 is an apocalyptic number.

21279647 is a deficient number, since it is larger than the sum of its proper divisors (48913).

21279647 is an equidigital number, since it uses as much as digits as its factorization.

21279647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 48912.

The product of its digits is 42336, while the sum is 38.

The square root of 21279647 is about 4612.9867764822. The cubic root of 21279647 is about 277.1116641555. Note that the first 3 decimals are identical.

The spelling of 21279647 in words is "twenty-one million, two hundred seventy-nine thousand, six hundred forty-seven".