21978371 has 4 divisors (see below), whose sum is σ = 22059744. Its totient is φ = 21897000.

The previous prime is 21978343. The next prime is 21978373. The reversal of 21978371 is 17387912.

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-21978371 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21978373) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40280 + ... + 40821.

It is an arithmetic number, because the mean of its divisors is an integer number (5514936).

Almost surely, 2^21978371 is an apocalyptic number.

21978371 is a deficient number, since it is larger than the sum of its proper divisors (81373).

21978371 is an equidigital number, since it uses as much as digits as its factorization.

21978371 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 81372.

The product of its digits is 21168, while the sum is 38.

The square root of 21978371 is about 4688.1095337033. The cubic root of 21978371 is about 280.1120767312.

The spelling of 21978371 in words is "twenty-one million, nine hundred seventy-eight thousand, three hundred seventy-one".