21071066491 has 4 divisors (see below), whose sum is σ = 21584994984. Its totient is φ = 20557138000.

The previous prime is 21071066479. The next prime is 21071066503. The reversal of 21071066491 is 19466017012.

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

It is an interprime number because it is at equal distance from previous prime (21071066479) and next prime (21071066503).

It is a cyclic number.

It is not a de Polignac number, because 21071066491 - 2⁹ = 21071065979 is a prime.

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 21071066491.

It is not an unprimeable number, because it can be changed into a prime (21071066431) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 256964185 + ... + 256964266.

It is an arithmetic number, because the mean of its divisors is an integer number (5396248746).

Almost surely, 2^21071066491 is an apocalyptic number.

21071066491 is a deficient number, since it is larger than the sum of its proper divisors (513928493).

21071066491 is an equidigital number, since it uses as much as digits as its factorization.

21071066491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 513928492.

The product of its (nonzero) digits is 18144, while the sum is 37.

The spelling of 21071066491 in words is "twenty-one billion, seventy-one million, sixty-six thousand, four hundred ninety-one".