21681932041661 has 4 divisors (see below), whose sum is σ = 21689877054300. Its totient is φ = 21673987029024.

The previous prime is 21681932041657. The next prime is 21681932041673. The reversal of 21681932041661 is 16614023918612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 16903034368900 + 4778897672761 = 4111330^2 + 2186069^2 .

It is a cyclic number.

It is not a de Polignac number, because 21681932041661 - 2² = 21681932041657 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681932071661) 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, 3972502226 + ... + 3972507683.

It is an arithmetic number, because the mean of its divisors is an integer number (5422469263575).

Almost surely, 2^{21681932041661} is an apocalyptic number.

It is an amenable number.

21681932041661 is a deficient number, since it is larger than the sum of its proper divisors (7945012639).

21681932041661 is an equidigital number, since it uses as much as digits as its factorization.

21681932041661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7945012638.

The product of its (nonzero) digits is 746496, while the sum is 50.

The spelling of 21681932041661 in words is "twenty-one trillion, six hundred eighty-one billion, nine hundred thirty-two million, forty-one thousand, six hundred sixty-one".