21001111081 has 2 divisors, whose sum is σ = 21001111082. Its totient is φ = 21001111080.

The previous prime is 21001111067. The next prime is 21001111181. The reversal of 21001111081 is 18011110012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20540622400 + 460488681 = 143320^2 + 21459^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001111081 - 2¹⁷ = 21000980009 is a prime.

It is a super-3 number, since 3×21001111081³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is not a weakly prime, because it can be changed into another prime (21001111181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500555540 + 10500555541.

It is an arithmetic number, because the mean of its divisors is an integer number (10500555541).

Almost surely, 2^21001111081 is an apocalyptic number.

It is an amenable number.

21001111081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001111081 is an equidigital number, since it uses as much as digits as its factorization.

21001111081 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16, while the sum is 16.

Adding to 21001111081 its reverse (18011110012), we get a palindrome (39012221093).

The spelling of 21001111081 in words is "twenty-one billion, one million, one hundred eleven thousand, eighty-one".