21781716373 has 4 divisors (see below), whose sum is σ = 21782092608. Its totient is φ = 21781340140.

The previous prime is 21781716371. The next prime is 21781716389. The reversal of 21781716373 is 37361718712.

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 21781716373 - 2¹ = 21781716371 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21781716371) 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, 80911 + ... + 223852.

It is an arithmetic number, because the mean of its divisors is an integer number (5445523152).

Almost surely, 2^21781716373 is an apocalyptic number.

It is an amenable number.

21781716373 is a deficient number, since it is larger than the sum of its proper divisors (376235).

21781716373 is an equidigital number, since it uses as much as digits as its factorization.

21781716373 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 376234.

The product of its digits is 296352, while the sum is 46.

The spelling of 21781716373 in words is "twenty-one billion, seven hundred eighty-one million, seven hundred sixteen thousand, three hundred seventy-three".