21000101111981 has 2 divisors, whose sum is σ = 21000101111982. Its totient is φ = 21000101111980.

The previous prime is 21000101111921. The next prime is 21000101111989. The reversal of 21000101111981 is 18911110100012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18725611836100 + 2274489275881 = 4327310^2 + 1508141^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000101111981 - 2³⁰ = 20999027370157 is a prime.

It is a super-2 number, since 2×21000101111981² (a number of 27 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21000101111981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21000101111989) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500050555990 + 10500050555991.

It is an arithmetic number, because the mean of its divisors is an integer number (10500050555991).

Almost surely, 2^{21000101111981} is an apocalyptic number.

It is an amenable number.

21000101111981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000101111981 is an equidigital number, since it uses as much as digits as its factorization.

21000101111981 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 26.

Adding to 21000101111981 its reverse (18911110100012), we get a palindrome (39911211211993).

The spelling of 21000101111981 in words is "twenty-one trillion, one hundred one million, one hundred eleven thousand, nine hundred eighty-one".