21785920 has 56 divisors (see below), whose sum is σ = 55878984. Its totient is φ = 8042496.

The previous prime is 21785917. The next prime is 21785947. The reversal of 21785920 is 2958712.

It can be written as a sum of positive squares in 4 ways, for example, as 2214144 + 19571776 = 1488^2 + 4424^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1542 + ... + 6778.

It is an arithmetic number, because the mean of its divisors is an integer number (997839).

Almost surely, 2^21785920 is an apocalyptic number.

21785920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21785920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27939492).

21785920 is an abundant number, since it is smaller than the sum of its proper divisors (34093064).

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

21785920 is a wasteful number, since it uses less digits than its factorization.

21785920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5267 (or 5257 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 21785920 is about 4667.5389660934. The cubic root of 21785920 is about 279.2920892823.

The spelling of 21785920 in words is "twenty-one million, seven hundred eighty-five thousand, nine hundred twenty".