21947278 has 4 divisors (see below), whose sum is σ = 32920920. Its totient is φ = 10973638.

The previous prime is 21947273. The next prime is 21947279. The reversal of 21947278 is 87274912.

It is a semiprime because it is the product of two primes.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 21947278.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21947273) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5486818 + ... + 5486821.

It is an arithmetic number, because the mean of its divisors is an integer number (8230230).

Almost surely, 2^21947278 is an apocalyptic number.

21947278 is a deficient number, since it is larger than the sum of its proper divisors (10973642).

21947278 is a wasteful number, since it uses less digits than its factorization.

21947278 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10973641.

The product of its digits is 56448, while the sum is 40.

The square root of 21947278 is about 4684.7922045700. The cubic root of 21947278 is about 279.9799220297.

The spelling of 21947278 in words is "twenty-one million, nine hundred forty-seven thousand, two hundred seventy-eight".