21001109081 has 2 divisors, whose sum is σ = 21001109082. Its totient is φ = 21001109080.

The previous prime is 21001109039. The next prime is 21001109111. The reversal of 21001109081 is 18090110012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14414163481 + 6586945600 = 120059^2 + 81160^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21001109081 is a prime.

It is a super-2 number, since 2×21001109081² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21001109021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500554540 + 10500554541.

It is an arithmetic number, because the mean of its divisors is an integer number (10500554541).

Almost surely, 2^21001109081 is an apocalyptic number.

It is an amenable number.

21001109081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001109081 is an equidigital number, since it uses as much as digits as its factorization.

21001109081 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 23.

Adding to 21001109081 its reverse (18090110012), we get a palindrome (39091219093).

The spelling of 21001109081 in words is "twenty-one billion, one million, one hundred nine thousand, eighty-one".