20981327681 has 2 divisors, whose sum is σ = 20981327682. Its totient is φ = 20981327680.

The previous prime is 20981327677. The next prime is 20981327687. The reversal of 20981327681 is 18672318902.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11361641281 + 9619686400 = 106591^2 + 98080^2 .

It is a cyclic number.

It is not a de Polignac number, because 20981327681 - 2² = 20981327677 is a prime.

It is a super-2 number, since 2×20981327681² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20981327687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10490663840 + 10490663841.

It is an arithmetic number, because the mean of its divisors is an integer number (10490663841).

Almost surely, 2^20981327681 is an apocalyptic number.

It is an amenable number.

20981327681 is a deficient number, since it is larger than the sum of its proper divisors (1).

20981327681 is an equidigital number, since it uses as much as digits as its factorization.

20981327681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 290304, while the sum is 47.

The spelling of 20981327681 in words is "twenty billion, nine hundred eighty-one million, three hundred twenty-seven thousand, six hundred eighty-one".