21540021 has 8 divisors (see below), whose sum is σ = 28743744. Its totient is φ = 14348160.

The previous prime is 21540019. The next prime is 21540023. The reversal of 21540021 is 12004512.

It is an interprime number because it is at equal distance from previous prime (21540019) and next prime (21540023).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21540021 - 2¹ = 21540019 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21540023) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2976 + ... + 7206.

It is an arithmetic number, because the mean of its divisors is an integer number (3592968).

Almost surely, 2^21540021 is an apocalyptic number.

It is an amenable number.

21540021 is a deficient number, since it is larger than the sum of its proper divisors (7203723).

21540021 is a wasteful number, since it uses less digits than its factorization.

21540021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5931.

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21540021 is about 4641.1228167330. The cubic root of 21540021 is about 278.2373152571.

Adding to 21540021 its reverse (12004512), we get a palindrome (33544533).

The spelling of 21540021 in words is "twenty-one million, five hundred forty thousand, twenty-one".