21205123541 has 8 divisors (see below), whose sum is σ = 24236948544. Its totient is φ = 18173928960.

The previous prime is 21205123531. The next prime is 21205123549. The reversal of 21205123541 is 14532150212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21205123541 - 2¹⁰ = 21205122517 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 21205123541.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205123549) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 83180 + ... + 222101.

It is an arithmetic number, because the mean of its divisors is an integer number (3029618568).

Almost surely, 2^21205123541 is an apocalyptic number.

It is an amenable number.

21205123541 is a deficient number, since it is larger than the sum of its proper divisors (3031825003).

21205123541 is an equidigital number, since it uses as much as digits as its factorization.

21205123541 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 315211.

The product of its (nonzero) digits is 2400, while the sum is 26.

Adding to 21205123541 its reverse (14532150212), we get a palindrome (35737273753).

The spelling of 21205123541 in words is "twenty-one billion, two hundred five million, one hundred twenty-three thousand, five hundred forty-one".