21785890 has 48 divisors (see below), whose sum is σ = 46059192. Its totient is φ = 7397376.

The previous prime is 21785867. The next prime is 21785903. The reversal of 21785890 is 9858712.

It can be written as a sum of positive squares in 4 ways, for example, as 21538881 + 247009 = 4641^2 + 497^2 .

It is an unprimeable number.

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 23 ways as a sum of consecutive naturals, for example, 84642 + ... + 84898.

Almost surely, 2^21785890 is an apocalyptic number.

21785890 is an abundant number, since it is smaller than the sum of its proper divisors (24273302).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21785890 is a wasteful number, since it uses less digits than its factorization.

21785890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 451 (or 444 counting only the distinct ones).

The product of its (nonzero) digits is 40320, while the sum is 40.

The square root of 21785890 is about 4667.5357524073. The cubic root of 21785890 is about 279.2919610838.

The spelling of 21785890 in words is "twenty-one million, seven hundred eighty-five thousand, eight hundred ninety".