21787289 has 8 divisors (see below), whose sum is σ = 22149000. Its totient is φ = 21428352.

The previous prime is 21787237. The next prime is 21787301. The reversal of 21787289 is 98278712.

It can be written as a sum of positive squares in 4 ways, for example, as 4481689 + 17305600 = 2117^2 + 4160^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21787289 - 2²⁴ = 5010073 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21787219) 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, 19847 + ... + 20915.

It is an arithmetic number, because the mean of its divisors is an integer number (2768625).

Almost surely, 2^21787289 is an apocalyptic number.

It is an amenable number.

21787289 is a deficient number, since it is larger than the sum of its proper divisors (361711).

21787289 is a wasteful number, since it uses less digits than its factorization.

21787289 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1387.

The product of its digits is 112896, while the sum is 44.

The square root of 21787289 is about 4667.6856149488. The cubic root of 21787289 is about 279.2979392817.

The spelling of 21787289 in words is "twenty-one million, seven hundred eighty-seven thousand, two hundred eighty-nine".