21987271 has 4 divisors (see below), whose sum is σ = 21998200. Its totient is φ = 21976344.

The previous prime is 21987269. The next prime is 21987293. The reversal of 21987271 is 17278912.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21987271 - 2¹ = 21987269 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 21987271.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987221) 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, 1476 + ... + 6793.

It is an arithmetic number, because the mean of its divisors is an integer number (5499550).

Almost surely, 2^21987271 is an apocalyptic number.

21987271 is a deficient number, since it is larger than the sum of its proper divisors (10929).

21987271 is an equidigital number, since it uses as much as digits as its factorization.

21987271 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10928.

The product of its digits is 14112, while the sum is 37.

The square root of 21987271 is about 4689.0586475326. The cubic root of 21987271 is about 280.1498814902.

The spelling of 21987271 in words is "twenty-one million, nine hundred eighty-seven thousand, two hundred seventy-one".