21001802158081 has 4 divisors (see below), whose sum is σ = 21398062576212. Its totient is φ = 20605541739952.

The previous prime is 21001802158079. The next prime is 21001802158109. The reversal of 21001802158081 is 18085120810012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 19124956957681 + 1876845200400 = 4373209^2 + 1369980^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001802158081 - 2¹ = 21001802158079 is a prime.

It is a super-2 number, since 2×21001802158081² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21001802158081.

It is not an unprimeable number, because it can be changed into a prime (21001802158021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 198130208986 + ... + 198130209091.

It is an arithmetic number, because the mean of its divisors is an integer number (5349515644053).

Almost surely, 2^{21001802158081} is an apocalyptic number.

It is an amenable number.

21001802158081 is a deficient number, since it is larger than the sum of its proper divisors (396260418131).

21001802158081 is an equidigital number, since it uses as much as digits as its factorization.

21001802158081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 396260418130.

The product of its (nonzero) digits is 10240, while the sum is 37.

Adding to 21001802158081 its reverse (18085120810012), we get a palindrome (39086922968093).

The spelling of 21001802158081 in words is "twenty-one trillion, one billion, eight hundred two million, one hundred fifty-eight thousand, eighty-one".