21530681 has 4 divisors (see below), whose sum is σ = 21721332. Its totient is φ = 21340032.

The previous prime is 21530671. The next prime is 21530701. The reversal of 21530681 is 18603512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11162281 + 10368400 = 3341^2 + 3220^2 .

It is a cyclic number.

It is not a de Polignac number, because 21530681 - 2²² = 17336377 is a prime.

It is a super-2 number, since 2×21530681² = 927140448647522, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21530681.

It is not an unprimeable number, because it can be changed into a prime (21530671) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 95156 + ... + 95381.

It is an arithmetic number, because the mean of its divisors is an integer number (5430333).

Almost surely, 2^21530681 is an apocalyptic number.

It is an amenable number.

21530681 is a deficient number, since it is larger than the sum of its proper divisors (190651).

21530681 is a wasteful number, since it uses less digits than its factorization.

21530681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 190650.

The product of its (nonzero) digits is 1440, while the sum is 26.

The square root of 21530681 is about 4640.1164856068. The cubic root of 21530681 is about 278.1970938133.

The spelling of 21530681 in words is "twenty-one million, five hundred thirty thousand, six hundred eighty-one".