21661699809856 has 28 divisors (see below), whose sum is σ = 43467912375660. Its totient is φ = 10709154959360.

The previous prime is 21661699809839. The next prime is 21661699809857. The reversal of 21661699809856 is 65890899616612.

It can be written as a sum of positive squares in 2 ways, for example, as 6284447334400 + 15377252475456 = 2506880^2 + 3921384^2 .

It is not an unprimeable number, because it can be changed into a prime (21661699809857) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1901477785 + ... + 1901489176.

Almost surely, 2^{21661699809856} is an apocalyptic number.

It is an amenable number.

21661699809856 is an abundant number, since it is smaller than the sum of its proper divisors (21806212565804).

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

21661699809856 is an equidigital number, since it uses as much as digits as its factorization.

21661699809856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3802967062 (or 3802967052 counting only the distinct ones).

The product of its (nonzero) digits is 604661760, while the sum is 76.

The spelling of 21661699809856 in words is "twenty-one trillion, six hundred sixty-one billion, six hundred ninety-nine million, eight hundred nine thousand, eight hundred fifty-six".