21010111981 has 2 divisors, whose sum is σ = 21010111982. Its totient is φ = 21010111980.

The previous prime is 21010111961. The next prime is 21010112017. The reversal of 21010111981 is 18911101012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16411915881 + 4598196100 = 128109^2 + 67810^2 .

It is a cyclic number.

It is not a de Polignac number, because 21010111981 - 2¹⁹ = 21009587693 is a prime.

It is a super-2 number, since 2×21010111981² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21010111901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505055990 + 10505055991.

It is an arithmetic number, because the mean of its divisors is an integer number (10505055991).

Almost surely, 2^21010111981 is an apocalyptic number.

It is an amenable number.

21010111981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21010111981 is an equidigital number, since it uses as much as digits as its factorization.

21010111981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 144, while the sum is 25.

Adding to 21010111981 its reverse (18911101012), we get a palindrome (39921212993).

The spelling of 21010111981 in words is "twenty-one billion, ten million, one hundred eleven thousand, nine hundred eighty-one".