21581136 has 60 divisors (see below), whose sum is σ = 61254388. Its totient is φ = 7091712.

The previous prime is 21581111. The next prime is 21581137. The reversal of 21581136 is 63118512.

It can be written as a sum of positive squares in 2 ways, for example, as 11696400 + 9884736 = 3420^2 + 3144^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21581137) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9486 + ... + 11538.

Almost surely, 2^21581136 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21581136, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30627194).

21581136 is an abundant number, since it is smaller than the sum of its proper divisors (39673252).

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

21581136 is a wasteful number, since it uses less digits than its factorization.

21581136 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2140 (or 2131 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 21581136 is about 4645.5501288868. The cubic root of 21581136 is about 278.4142333191.

Adding to 21581136 its reverse (63118512), we get a palindrome (84699648).

The spelling of 21581136 in words is "twenty-one million, five hundred eighty-one thousand, one hundred thirty-six".