21172343721 has 4 divisors (see below), whose sum is σ = 28229791632. Its totient is φ = 14114895812.

The previous prime is 21172343719. The next prime is 21172343771. The reversal of 21172343721 is 12734327112.

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 21172343721 - 2¹ = 21172343719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21172343771) 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, 3528723951 + ... + 3528723956.

It is an arithmetic number, because the mean of its divisors is an integer number (7057447908).

Almost surely, 2^21172343721 is an apocalyptic number.

It is an amenable number.

21172343721 is a deficient number, since it is larger than the sum of its proper divisors (7057447911).

21172343721 is an equidigital number, since it uses as much as digits as its factorization.

21172343721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7057447910.

The product of its digits is 14112, while the sum is 33.

The spelling of 21172343721 in words is "twenty-one billion, one hundred seventy-two million, three hundred forty-three thousand, seven hundred twenty-one".