21681980681 has 4 divisors (see below), whose sum is σ = 21683537172. Its totient is φ = 21680424192.

The previous prime is 21681980627. The next prime is 21681980713. The reversal of 21681980681 is 18608918612.

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 1981051081 + 19700929600 = 44509^2 + 140360^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21681980681 is a prime.

It is a super-3 number, since 3×21681980681³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21681980611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 757160 + ... + 785273.

It is an arithmetic number, because the mean of its divisors is an integer number (5420884293).

Almost surely, 2^21681980681 is an apocalyptic number.

It is an amenable number.

21681980681 is a deficient number, since it is larger than the sum of its proper divisors (1556491).

21681980681 is a wasteful number, since it uses less digits than its factorization.

21681980681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1556490.

The product of its (nonzero) digits is 331776, while the sum is 50.

The spelling of 21681980681 in words is "twenty-one billion, six hundred eighty-one million, nine hundred eighty thousand, six hundred eighty-one".