21643591081 has 16 divisors (see below), whose sum is σ = 25332334848. Its totient is φ = 18109224000.

The previous prime is 21643591051. The next prime is 21643591111. The reversal of 21643591081 is 18019534612.

It is an interprime number because it is at equal distance from previous prime (21643591051) and next prime (21643591111).

It is not a de Polignac number, because 21643591081 - 2¹⁹ = 21643066793 is a prime.

It is a super-2 number, since 2×21643591081² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21643591001) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 165390 + ... + 265783.

It is an arithmetic number, because the mean of its divisors is an integer number (1583270928).

Almost surely, 2^21643591081 is an apocalyptic number.

It is an amenable number.

21643591081 is a deficient number, since it is larger than the sum of its proper divisors (3688743767).

21643591081 is a wasteful number, since it uses less digits than its factorization.

21643591081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 431352.

The product of its (nonzero) digits is 51840, while the sum is 40.

The spelling of 21643591081 in words is "twenty-one billion, six hundred forty-three million, five hundred ninety-one thousand, eighty-one".