21543761 has 4 divisors (see below), whose sum is σ = 21688500. Its totient is φ = 21399024.

The previous prime is 21543757. The next prime is 21543779. The reversal of 21543761 is 16734512.

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 2890000 + 18653761 = 1700^2 + 4319^2 .

It is a cyclic number.

It is not a de Polignac number, because 21543761 - 2² = 21543757 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21543721) 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, 72146 + ... + 72443.

It is an arithmetic number, because the mean of its divisors is an integer number (5422125).

Almost surely, 2^21543761 is an apocalyptic number.

It is an amenable number.

21543761 is a deficient number, since it is larger than the sum of its proper divisors (144739).

21543761 is a wasteful number, since it uses less digits than its factorization.

21543761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144738.

The product of its digits is 5040, while the sum is 29.

The square root of 21543761 is about 4641.5257189851. The cubic root of 21543761 is about 278.2534178000.

Subtracting from 21543761 its reverse (16734512), we obtain a square (4809249 = 2193²).

The spelling of 21543761 in words is "twenty-one million, five hundred forty-three thousand, seven hundred sixty-one".