21101111981 has 2 divisors, whose sum is σ = 21101111982. Its totient is φ = 21101111980.

The previous prime is 21101111893. The next prime is 21101112007. The reversal of 21101111981 is 18911110112.

It is an a-pointer prime, because the next prime (21101112007) can be obtained adding 21101111981 to its sum of digits (26).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18449788900 + 2651323081 = 135830^2 + 51491^2 .

It is a cyclic number.

It is not a de Polignac number, because 21101111981 - 2³⁰ = 20027370157 is a prime.

It is a super-2 number, since 2×21101111981² (a number of 21 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21101111981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21101111081) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10550555990 + 10550555991.

It is an arithmetic number, because the mean of its divisors is an integer number (10550555991).

Almost surely, 2^21101111981 is an apocalyptic number.

It is an amenable number.

21101111981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21101111981 is an equidigital number, since it uses as much as digits as its factorization.

21101111981 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.

The spelling of 21101111981 in words is "twenty-one billion, one hundred one million, one hundred eleven thousand, nine hundred eighty-one".