21206221680 has 160 divisors (see below), whose sum is σ = 75176331264. Its totient is φ = 4844187648.

The previous prime is 21206221649. The next prime is 21206221681. The reversal of 21206221680 is 8612260212.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21206221681) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4000792 + ... + 4006088.

Almost surely, 2^21206221680 is an apocalyptic number.

21206221680 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21206221680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37588165632).

21206221680 is an abundant number, since it is smaller than the sum of its proper divisors (53970109584).

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

21206221680 is a wasteful number, since it uses less digits than its factorization.

21206221680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7703 (or 7697 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 30.

Adding to 21206221680 its reverse (8612260212), we get a palindrome (29818481892).

The spelling of 21206221680 in words is "twenty-one billion, two hundred six million, two hundred twenty-one thousand, six hundred eighty".