21173312561 has 8 divisors (see below), whose sum is σ = 22096559040. Its totient is φ = 20250288432.

The previous prime is 21173312551. The next prime is 21173312569. The reversal of 21173312561 is 16521337112.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21173312561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21173312569) 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, 156230 + ... + 258368.

It is an arithmetic number, because the mean of its divisors is an integer number (2762069880).

Almost surely, 2^21173312561 is an apocalyptic number.

It is an amenable number.

21173312561 is a deficient number, since it is larger than the sum of its proper divisors (923246479).

21173312561 is a wasteful number, since it uses less digits than its factorization.

21173312561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 111175.

The product of its digits is 7560, while the sum is 32.

Adding to 21173312561 its reverse (16521337112), we get a palindrome (37694649673).

The spelling of 21173312561 in words is "twenty-one billion, one hundred seventy-three million, three hundred twelve thousand, five hundred sixty-one".