21778855 has 32 divisors (see below), whose sum is σ = 31680000. Its totient is φ = 14055552.

The previous prime is 21778843. The next prime is 21778859. The reversal of 21778855 is 55887712.

It is not a de Polignac number, because 21778855 - 2⁷ = 21778727 is a prime.

It is a super-2 number, since 2×21778855² = 948637050222050, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (43).

It is a congruent number.

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

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 43396 + ... + 43894.

It is an arithmetic number, because the mean of its divisors is an integer number (990000).

Almost surely, 2^21778855 is an apocalyptic number.

21778855 is a deficient number, since it is larger than the sum of its proper divisors (9901145).

21778855 is a wasteful number, since it uses less digits than its factorization.

21778855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 583.

The product of its digits is 156800, while the sum is 43.

The square root of 21778855 is about 4666.7820819061. The cubic root of 21778855 is about 279.2618952862.

The spelling of 21778855 in words is "twenty-one million, seven hundred seventy-eight thousand, eight hundred fifty-five".