21657602721 has 8 divisors (see below), whose sum is σ = 28879877824. Its totient is φ = 14436864720.

The previous prime is 21657602719. The next prime is 21657602749. The reversal of 21657602721 is 12720675612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21657602721 - 2¹ = 21657602719 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21657602721.

It is not an unprimeable number, because it can be changed into a prime (21657602711) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 350986 + ... + 408051.

It is an arithmetic number, because the mean of its divisors is an integer number (3609984728).

Almost surely, 2^21657602721 is an apocalyptic number.

It is an amenable number.

21657602721 is a deficient number, since it is larger than the sum of its proper divisors (7222275103).

21657602721 is an equidigital number, since it uses as much as digits as its factorization.

21657602721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 768551.

The product of its (nonzero) digits is 70560, while the sum is 39.

The spelling of 21657602721 in words is "twenty-one billion, six hundred fifty-seven million, six hundred two thousand, seven hundred twenty-one".