21540321 has 12 divisors (see below), whose sum is σ = 33942480. Its totient is φ = 13054680.

The previous prime is 21540317. The next prime is 21540341. The reversal of 21540321 is 12304512.

It is not a de Polignac number, because 21540321 - 2² = 21540317 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21540294 and 21540303.

It is not an unprimeable number, because it can be changed into a prime (21540341) 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, 108691 + ... + 108888.

It is an arithmetic number, because the mean of its divisors is an integer number (2828540).

Almost surely, 2^21540321 is an apocalyptic number.

It is an amenable number.

21540321 is a deficient number, since it is larger than the sum of its proper divisors (12402159).

21540321 is a wasteful number, since it uses less digits than its factorization.

21540321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 217596 (or 217593 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21540321 is about 4641.1551363858. The cubic root of 21540321 is about 278.2386069736.

Adding to 21540321 its reverse (12304512), we get a palindrome (33844833).

The spelling of 21540321 in words is "twenty-one million, five hundred forty thousand, three hundred twenty-one".