21778859 has 2 divisors, whose sum is σ = 21778860. Its totient is φ = 21778858.

The previous prime is 21778843. The next prime is 21778873. The reversal of 21778859 is 95887712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21778859 - 2⁴ = 21778843 is a prime.

It is not a weakly prime, because it can be changed into another prime (21778879) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10889429 + 10889430.

It is an arithmetic number, because the mean of its divisors is an integer number (10889430).

Almost surely, 2^21778859 is an apocalyptic number.

21778859 is a deficient number, since it is larger than the sum of its proper divisors (1).

21778859 is an equidigital number, since it uses as much as digits as its factorization.

21778859 is an evil number, because the sum of its binary digits is even.

The product of its digits is 282240, while the sum is 47.

The square root of 21778859 is about 4666.7825104669. The cubic root of 21778859 is about 279.2619123830.

The spelling of 21778859 in words is "twenty-one million, seven hundred seventy-eight thousand, eight hundred fifty-nine".