21778857 has 6 divisors (see below), whose sum is σ = 31458362. Its totient is φ = 14519232.

The previous prime is 21778843. The next prime is 21778859. The reversal of 21778857 is 75887712.

It can be written as a sum of positive squares in only one way, i.e., 18352656 + 3426201 = 4284^2 + 1851^2 .

It is not a de Polignac number, because 21778857 - 2⁶ = 21778793 is a prime.

It is a super-2 number, since 2×21778857² = 948637224452898, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21778859) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1209928 + ... + 1209945.

Almost surely, 2^21778857 is an apocalyptic number.

It is an amenable number.

21778857 is a deficient number, since it is larger than the sum of its proper divisors (9679505).

21778857 is a wasteful number, since it uses less digits than its factorization.

21778857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2419879 (or 2419876 counting only the distinct ones).

The product of its digits is 219520, while the sum is 45.

The square root of 21778857 is about 4666.7822961865. The cubic root of 21778857 is about 279.2619038346.

The spelling of 21778857 in words is "twenty-one million, seven hundred seventy-eight thousand, eight hundred fifty-seven".