21543381 has 16 divisors (see below), whose sum is σ = 32395200. Its totient is φ = 14146704.

The previous prime is 21543373. The next prime is 21543407. The reversal of 21543381 is 18334512.

It is a happy number.

It is not a de Polignac number, because 21543381 - 2³ = 21543373 is a prime.

It is a super-2 number, since 2×21543381² = 928234529822322, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21543331) 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 15 ways as a sum of consecutive naturals, for example, 4146 + ... + 7763.

It is an arithmetic number, because the mean of its divisors is an integer number (2024700).

Almost surely, 2^21543381 is an apocalyptic number.

It is an amenable number.

21543381 is a deficient number, since it is larger than the sum of its proper divisors (10851819).

21543381 is a wasteful number, since it uses less digits than its factorization.

21543381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11985 (or 11979 counting only the distinct ones).

The product of its digits is 2880, while the sum is 27.

The square root of 21543381 is about 4641.4847839888. The cubic root of 21543381 is about 278.2517817978.

Adding to 21543381 its reverse (18334512), we get a palindrome (39877893).

The spelling of 21543381 in words is "twenty-one million, five hundred forty-three thousand, three hundred eighty-one".