21978023 has 2 divisors, whose sum is σ = 21978024. Its totient is φ = 21978022.

The previous prime is 21978017. The next prime is 21978043. The reversal of 21978023 is 32087912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21978023 - 2⁴ = 21978007 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21978043) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10989011 + 10989012.

It is an arithmetic number, because the mean of its divisors is an integer number (10989012).

Almost surely, 2^21978023 is an apocalyptic number.

21978023 is a deficient number, since it is larger than the sum of its proper divisors (1).

21978023 is an equidigital number, since it uses as much as digits as its factorization.

21978023 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6048, while the sum is 32.

The square root of 21978023 is about 4688.0724183826. The cubic root of 21978023 is about 280.1105983154.

The spelling of 21978023 in words is "twenty-one million, nine hundred seventy-eight thousand, twenty-three".