21011009789981 has 2 divisors, whose sum is σ = 21011009789982. Its totient is φ = 21011009789980.

The previous prime is 21011009789971. The next prime is 21011009789999. The reversal of 21011009789981 is 18998790011012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19613684842756 + 1397324947225 = 4428734^2 + 1182085^2 .

It is a cyclic number.

It is not a de Polignac number, because 21011009789981 - 2³⁴ = 20993829920797 is a prime.

It is a super-2 number, since 2×21011009789981² (a number of 27 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21011009789971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505504894990 + 10505504894991.

It is an arithmetic number, because the mean of its divisors is an integer number (10505504894991).

Almost surely, 2^{21011009789981} is an apocalyptic number.

It is an amenable number.

21011009789981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21011009789981 is an equidigital number, since it uses as much as digits as its factorization.

21011009789981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 653184, while the sum is 56.

The spelling of 21011009789981 in words is "twenty-one trillion, eleven billion, nine million, seven hundred eighty-nine thousand, nine hundred eighty-one".