21720050208 has 180 divisors, whose sum is σ = 65661884442. Its totient is φ = 7043189760.

The previous prime is 21720050173. The next prime is 21720050213. The reversal of 21720050208 is 80205002712.

It can be written as a sum of positive squares in 3 ways, for example, as 21184220304 + 535829904 = 145548^2 + 23148^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 3545388 + ... + 3551508.

Almost surely, 2^21720050208 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21720050208, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32830942221).

21720050208 is an abundant number, since it is smaller than the sum of its proper divisors (43941834234).

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

21720050208 is an equidigital number, since it uses as much as digits as its factorization.

21720050208 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6217 (or 6163 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 27.

The spelling of 21720050208 in words is "twenty-one billion, seven hundred twenty million, fifty thousand, two hundred eight".