21685737520 has 80 divisors (see below), whose sum is σ = 52094880000. Its totient is φ = 8386560000.

The previous prime is 21685737487. The next prime is 21685737529. The reversal of 21685737520 is 2573758612.

It is a tau number, because it is divible by the number of its divisors (80).

It is not an unprimeable number, because it can be changed into a prime (21685737529) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3094020 + ... + 3101020.

It is an arithmetic number, because the mean of its divisors is an integer number (651186000).

Almost surely, 2^21685737520 is an apocalyptic number.

21685737520 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 21685737520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26047440000).

21685737520 is an abundant number, since it is smaller than the sum of its proper divisors (30409142480).

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

21685737520 is a wasteful number, since it uses less digits than its factorization.

21685737520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8294 (or 8288 counting only the distinct ones).

The product of its (nonzero) digits is 705600, while the sum is 46.

The spelling of 21685737520 in words is "twenty-one billion, six hundred eighty-five million, seven hundred thirty-seven thousand, five hundred twenty".