21778291 has 4 divisors (see below), whose sum is σ = 21789072. Its totient is φ = 21767512.

The previous prime is 21778279. The next prime is 21778297. The reversal of 21778291 is 19287712.

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 21778291 - 2⁵ = 21778259 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 21778291.

It is not an unprimeable number, because it can be changed into a prime (21778297) 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, 1351 + ... + 6736.

It is an arithmetic number, because the mean of its divisors is an integer number (5447268).

Almost surely, 2^21778291 is an apocalyptic number.

21778291 is a deficient number, since it is larger than the sum of its proper divisors (10781).

21778291 is an equidigital number, since it uses as much as digits as its factorization.

21778291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10780.

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

The square root of 21778291 is about 4666.7216544379. The cubic root of 21778291 is about 279.2594846136.

The spelling of 21778291 in words is "twenty-one million, seven hundred seventy-eight thousand, two hundred ninety-one".