21318628081 has 3 divisors (see below), whose sum is σ = 21318774091. Its totient is φ = 21318482072.

The previous prime is 21318627947. The next prime is 21318628091. The reversal of 21318628081 is 18082681312.

The square root of 21318628081 is 146009.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 8988746481 + 12329881600 = 94809^2 + 111040^2 .

It is not a de Polignac number, because 21318628081 - 2²⁷ = 21184410353 is a prime.

It is a super-2 number, since 2×21318628081² (a number of 21 digits) contains 22 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21318628091) 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 2 ways as a sum of consecutive naturals, for example, 73005 + ... + 219013.

Almost surely, 2^21318628081 is an apocalyptic number.

21318628081 is the 146009-th square number.

21318628081 is the 73005-th centered octagonal number.

It is an amenable number.

21318628081 is a deficient number, since it is larger than the sum of its proper divisors (146010).

21318628081 is an frugal number, since it uses more digits than its factorization.

21318628081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 292018 (or 146009 counting only the distinct ones).

The product of its (nonzero) digits is 36864, while the sum is 40.

Multiplying 21318628081 by its product of nonzero digits (36864), we get a square (785889905577984 = 28033728²).

The spelling of 21318628081 in words is "twenty-one billion, three hundred eighteen million, six hundred twenty-eight thousand, eighty-one".