21643541 has 4 divisors (see below), whose sum is σ = 22389900. Its totient is φ = 20897184.

The previous prime is 21643519. The next prime is 21643607. The reversal of 21643541 is 14534612.

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 15288100 + 6355441 = 3910^2 + 2521^2 .

It is a cyclic number.

It is not a de Polignac number, because 21643541 - 2¹⁴ = 21627157 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21643541.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21643841) 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, 373136 + ... + 373193.

It is an arithmetic number, because the mean of its divisors is an integer number (5597475).

Almost surely, 2^21643541 is an apocalyptic number.

It is an amenable number.

21643541 is a deficient number, since it is larger than the sum of its proper divisors (746359).

21643541 is an equidigital number, since it uses as much as digits as its factorization.

21643541 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 746358.

The product of its digits is 2880, while the sum is 26.

The square root of 21643541 is about 4652.2619229790. The cubic root of 21643541 is about 278.6823335120.

The spelling of 21643541 in words is "twenty-one million, six hundred forty-three thousand, five hundred forty-one".