21642647 has 8 divisors (see below), whose sum is σ = 23447760. Its totient is φ = 19975800.

The previous prime is 21642637. The next prime is 21642667. The reversal of 21642647 is 74624612.

It is not a de Polignac number, because 21642647 - 2²⁰ = 20594071 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 (21642637) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2729 + ... + 7122.

It is an arithmetic number, because the mean of its divisors is an integer number (2930970).

Almost surely, 2^21642647 is an apocalyptic number.

21642647 is a deficient number, since it is larger than the sum of its proper divisors (1805113).

21642647 is an frugal number, since it uses more digits than its factorization.

21642647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9890 (or 9864 counting only the distinct ones).

The product of its digits is 16128, while the sum is 32.

The square root of 21642647 is about 4652.1658396923. The cubic root of 21642647 is about 278.6784964098.

The spelling of 21642647 in words is "twenty-one million, six hundred forty-two thousand, six hundred forty-seven".