21540213 has 12 divisors (see below), whose sum is σ = 32466720. Its totient is φ = 13735656.

The previous prime is 21540209. The next prime is 21540217. The reversal of 21540213 is 31204512.

It is an interprime number because it is at equal distance from previous prime (21540209) and next prime (21540217).

It is not a de Polignac number, because 21540213 - 2² = 21540209 is a prime.

It is a super-3 number, since 3×21540213³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21540217) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 51823 + ... + 52236.

It is an arithmetic number, because the mean of its divisors is an integer number (2705560).

Almost surely, 2^21540213 is an apocalyptic number.

21540213 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

It is an amenable number.

21540213 is a deficient number, since it is larger than the sum of its proper divisors (10926507).

21540213 is a wasteful number, since it uses less digits than its factorization.

21540213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 104088 (or 104085 counting only the distinct ones).

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

The square root of 21540213 is about 4641.1435013367. The cubic root of 21540213 is about 278.2381419571.

Adding to 21540213 its reverse (31204512), we get a palindrome (52744725).

The spelling of 21540213 in words is "twenty-one million, five hundred forty thousand, two hundred thirteen".