21978769 has 4 divisors (see below), whose sum is σ = 21989044. Its totient is φ = 21968496.

The previous prime is 21978743. The next prime is 21978779. The reversal of 21978769 is 96787912.

It is a happy number.

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 can be written as a sum of positive squares in 2 ways, for example, as 16711744 + 5267025 = 4088^2 + 2295^2 .

It is a cyclic number.

It is not a de Polignac number, because 21978769 - 2⁷ = 21978641 is a prime.

It is a super-2 number, since 2×21978769² = 966132573510722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21978779) 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, 582 + ... + 6655.

It is an arithmetic number, because the mean of its divisors is an integer number (5497261).

Almost surely, 2^21978769 is an apocalyptic number.

It is an amenable number.

21978769 is a deficient number, since it is larger than the sum of its proper divisors (10275).

21978769 is an equidigital number, since it uses as much as digits as its factorization.

21978769 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10274.

The product of its digits is 381024, while the sum is 49.

The square root of 21978769 is about 4688.1519813248. The cubic root of 21978769 is about 280.1137675441.

The spelling of 21978769 in words is "twenty-one million, nine hundred seventy-eight thousand, seven hundred sixty-nine".