21506205516172 has 48 divisors (see below), whose sum is σ = 42955471444032. Its totient is φ = 9333273323520.

The previous prime is 21506205516163. The next prime is 21506205516247. The reversal of 21506205516172 is 27161550260512.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10503529 + ... + 12382912.

It is an arithmetic number, because the mean of its divisors is an integer number (894905655084).

Almost surely, 2^{21506205516172} is an apocalyptic number.

It is an amenable number.

21506205516172 is a deficient number, since it is larger than the sum of its proper divisors (21449265927860).

21506205516172 is a wasteful number, since it uses less digits than its factorization.

21506205516172 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22887538 (or 22887536 counting only the distinct ones).

The product of its (nonzero) digits is 252000, while the sum is 43.

Adding to 21506205516172 its reverse (27161550260512), we get a palindrome (48667755776684).

The spelling of 21506205516172 in words is "twenty-one trillion, five hundred six billion, two hundred five million, five hundred sixteen thousand, one hundred seventy-two".