21785580 has 72 divisors (see below), whose sum is σ = 66673152. Its totient is φ = 5757696.

The previous prime is 21785579. The next prime is 21785587. The reversal of 21785580 is 8558712.

21785580 is a `hidden beast` number, since 2 + 1 + 78 + 5 + 580 = 666.

It is a super-2 number, since 2×21785580² = 949222991872800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (21785587) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 22384 + ... + 23336.

It is an arithmetic number, because the mean of its divisors is an integer number (926016).

Almost surely, 2^21785580 is an apocalyptic number.

21785580 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 21785580, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33336576).

21785580 is an abundant number, since it is smaller than the sum of its proper divisors (44887572).

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

21785580 is a wasteful number, since it uses less digits than its factorization.

21785580 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1095 (or 1090 counting only the distinct ones).

The product of its (nonzero) digits is 22400, while the sum is 36.

The square root of 21785580 is about 4667.5025441878. The cubic root of 21785580 is about 279.2906363591.

The spelling of 21785580 in words is "twenty-one million, seven hundred eighty-five thousand, five hundred eighty".