21939647 has 4 divisors (see below), whose sum is σ = 22406496. Its totient is φ = 21472800.

The previous prime is 21939641. The next prime is 21939649. The reversal of 21939647 is 74693912.

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 21939647 - 2⁸ = 21939391 is a prime.

It is a super-2 number, since 2×21939647² = 962696220969218, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21939641) 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, 233354 + ... + 233447.

It is an arithmetic number, because the mean of its divisors is an integer number (5601624).

Almost surely, 2^21939647 is an apocalyptic number.

21939647 is a deficient number, since it is larger than the sum of its proper divisors (466849).

21939647 is an equidigital number, since it uses as much as digits as its factorization.

21939647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 466848.

The product of its digits is 81648, while the sum is 41.

The square root of 21939647 is about 4683.9776899554. The cubic root of 21939647 is about 279.9474688867.

The spelling of 21939647 in words is "twenty-one million, nine hundred thirty-nine thousand, six hundred forty-seven".