21721112084561 has 4 divisors (see below), whose sum is σ = 21854370441072. Its totient is φ = 21587853728052.

The previous prime is 21721112084527. The next prime is 21721112084563. The reversal of 21721112084561 is 16548021112712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21721112084561 - 2²² = 21721107890257 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21721112084563) 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, 66629178011 + ... + 66629178336.

It is an arithmetic number, because the mean of its divisors is an integer number (5463592610268).

Almost surely, 2^{21721112084561} is an apocalyptic number.

It is an amenable number.

21721112084561 is a deficient number, since it is larger than the sum of its proper divisors (133258356511).

21721112084561 is a wasteful number, since it uses less digits than its factorization.

21721112084561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 133258356510.

The product of its (nonzero) digits is 53760, while the sum is 41.

The spelling of 21721112084561 in words is "twenty-one trillion, seven hundred twenty-one billion, one hundred twelve million, eighty-four thousand, five hundred sixty-one".