21581730 has 48 divisors (see below), whose sum is σ = 57637944. Its totient is φ = 5598720.

The previous prime is 21581711. The next prime is 21581731. The reversal of 21581730 is 3718512.

It can be written as a sum of positive squares in 4 ways, for example, as 21538881 + 42849 = 4641^2 + 207^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21581694 and 21581703.

It is not an unprimeable number, because it can be changed into a prime (21581731) 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, 90 + ... + 6570.

Almost surely, 2^21581730 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21581730, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28818972).

21581730 is an abundant number, since it is smaller than the sum of its proper divisors (36056214).

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

21581730 is a wasteful number, since it uses less digits than its factorization.

21581730 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6531 (or 6528 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 21581730 is about 4645.6140605952. The cubic root of 21581730 is about 278.4167876569.

The spelling of 21581730 in words is "twenty-one million, five hundred eighty-one thousand, seven hundred thirty".