21981541081 has 2 divisors, whose sum is σ = 21981541082. Its totient is φ = 21981541080.

The previous prime is 21981541079. The next prime is 21981541103. The reversal of 21981541081 is 18014518912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21980731081 + 810000 = 148259^2 + 900^2 .

It is a cyclic number.

It is not a de Polignac number, because 21981541081 - 2¹ = 21981541079 is a prime.

It is a super-2 number, since 2×21981541081² (a number of 21 digits) contains 22 as substring.

Together with 21981541079, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21981541051) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10990770540 + 10990770541.

It is an arithmetic number, because the mean of its divisors is an integer number (10990770541).

Almost surely, 2^21981541081 is an apocalyptic number.

It is an amenable number.

21981541081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21981541081 is an equidigital number, since it uses as much as digits as its factorization.

21981541081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 23040, while the sum is 40.

The spelling of 21981541081 in words is "twenty-one billion, nine hundred eighty-one million, five hundred forty-one thousand, eighty-one".