21785280 has 112 divisors (see below), whose sum is σ = 75492864. Its totient is φ = 5278720.

The previous prime is 21785263. The next prime is 21785287. The reversal of 21785280 is 8258712.

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21785287) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9529 + ... + 11591.

Almost surely, 2^21785280 is an apocalyptic number.

21785280 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 21785280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37746432).

21785280 is an abundant number, since it is smaller than the sum of its proper divisors (53707584).

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

21785280 is a wasteful number, since it uses less digits than its factorization.

21785280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2094 (or 2084 counting only the distinct ones).

The product of its (nonzero) digits is 8960, while the sum is 33.

The square root of 21785280 is about 4667.4704069764. The cubic root of 21785280 is about 279.2893543555.

The spelling of 21785280 in words is "twenty-one million, seven hundred eighty-five thousand, two hundred eighty".