21721722217218 has 96 divisors (see below), whose sum is σ = 50085450005760. Its totient is φ = 6792212770560.

The previous prime is 21721722217187. The next prime is 21721722217229. The reversal of 21721722217218 is 81271222712712.

It is a happy number.

21721722217218 is a `hidden beast` number, since 2 + 1 + 7 + 217 + 2 + 2 + 217 + 218 = 666.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 129873 + ... + 6592443.

It is an arithmetic number, because the mean of its divisors is an integer number (521723437560).

Almost surely, 2^{21721722217218} is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21721722217218, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25042725002880).

21721722217218 is an abundant number, since it is smaller than the sum of its proper divisors (28363727788542).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21721722217218 is a wasteful number, since it uses less digits than its factorization.

21721722217218 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6462792 (or 6462789 counting only the distinct ones).

The product of its digits is 175616, while the sum is 45.

The spelling of 21721722217218 in words is "twenty-one trillion, seven hundred twenty-one billion, seven hundred twenty-two million, two hundred seventeen thousand, two hundred eighteen".