21705512620 has 144 divisors (see below), whose sum is σ = 55122778368. Its totient is φ = 7105162240.

The previous prime is 21705512611. The next prime is 21705512639. The reversal of 21705512620 is 2621550712.

It is a super-2 number, since 2×21705512620² (a number of 21 digits) contains 22 as substring.

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, 1454919 + ... + 1469761.

It is an arithmetic number, because the mean of its divisors is an integer number (382797072).

Almost surely, 2^21705512620 is an apocalyptic number.

21705512620 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 21705512620, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27561389184).

21705512620 is an abundant number, since it is smaller than the sum of its proper divisors (33417265748).

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

21705512620 is a wasteful number, since it uses less digits than its factorization.

21705512620 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14920 (or 14901 counting only the distinct ones).

The product of its (nonzero) digits is 8400, while the sum is 31.

The spelling of 21705512620 in words is "twenty-one billion, seven hundred five million, five hundred twelve thousand, six hundred twenty".