21978263 has 16 divisors (see below), whose sum is σ = 23950080. Its totient is φ = 20092800.

The previous prime is 21978251. The next prime is 21978293. The reversal of 21978263 is 36287912.

It is a cyclic number.

It is not a de Polignac number, because 21978263 - 2⁴ = 21978247 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21978293) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 158048 + ... + 158186.

It is an arithmetic number, because the mean of its divisors is an integer number (1496880).

Almost surely, 2^21978263 is an apocalyptic number.

21978263 is a deficient number, since it is larger than the sum of its proper divisors (1971817).

21978263 is a wasteful number, since it uses less digits than its factorization.

21978263 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 358.

The product of its digits is 36288, while the sum is 38.

The square root of 21978263 is about 4688.0980151870. The cubic root of 21978263 is about 280.1116179142. Note that the first 3 decimals are identical.

The spelling of 21978263 in words is "twenty-one million, nine hundred seventy-eight thousand, two hundred sixty-three".