21555512171 has 4 divisors (see below), whose sum is σ = 21588828912. Its totient is φ = 21522195432.

The previous prime is 21555512149. The next prime is 21555512189. The reversal of 21555512171 is 17121555512.

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 21555512171 - 2⁶ = 21555512107 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21555512191) 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, 16657400 + ... + 16658693.

It is an arithmetic number, because the mean of its divisors is an integer number (5397207228).

Almost surely, 2^21555512171 is an apocalyptic number.

21555512171 is a deficient number, since it is larger than the sum of its proper divisors (33316741).

21555512171 is an equidigital number, since it uses as much as digits as its factorization.

21555512171 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33316740.

The product of its digits is 17500, while the sum is 35.

The spelling of 21555512171 in words is "twenty-one billion, five hundred fifty-five million, five hundred twelve thousand, one hundred seventy-one".