21123010081 has 2 divisors, whose sum is σ = 21123010082. Its totient is φ = 21123010080.

The previous prime is 21123010079. The next prime is 21123010159. The reversal of 21123010081 is 18001032112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21036891681 + 86118400 = 145041^2 + 9280^2 .

It is a cyclic number.

It is not a de Polignac number, because 21123010081 - 2¹ = 21123010079 is a prime.

It is a super-2 number, since 2×21123010081² (a number of 21 digits) contains 22 as substring.

Together with 21123010079, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21123010681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561505040 + 10561505041.

It is an arithmetic number, because the mean of its divisors is an integer number (10561505041).

Almost surely, 2^21123010081 is an apocalyptic number.

It is an amenable number.

21123010081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123010081 is an equidigital number, since it uses as much as digits as its factorization.

21123010081 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 96, while the sum is 19.

Adding to 21123010081 its reverse (18001032112), we get a palindrome (39124042193).

The spelling of 21123010081 in words is "twenty-one billion, one hundred twenty-three million, ten thousand, eighty-one".