20561543 has 4 divisors (see below), whose sum is σ = 20606040. Its totient is φ = 20517048.

The previous prime is 20561533. The next prime is 20561549. The reversal of 20561543 is 34516502.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20561543 - 2¹² = 20557447 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20561549) 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, 21548 + ... + 22481.

It is an arithmetic number, because the mean of its divisors is an integer number (5151510).

Almost surely, 2^20561543 is an apocalyptic number.

20561543 is a deficient number, since it is larger than the sum of its proper divisors (44497).

20561543 is an equidigital number, since it uses as much as digits as its factorization.

20561543 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44496.

The product of its (nonzero) digits is 3600, while the sum is 26.

The square root of 20561543 is about 4534.4837633407. The cubic root of 20561543 is about 273.9587866689.

The spelling of 20561543 in words is "twenty million, five hundred sixty-one thousand, five hundred forty-three".