66721842791 has 4 divisors (see below), whose sum is σ = 66722592432. Its totient is φ = 66721093152.

The previous prime is 66721842787. The next prime is 66721842793. The reversal of 66721842791 is 19724812766.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 19724812766 = 2 ⋅9862406383.

It is a cyclic number.

It is not a de Polignac number, because 66721842791 - 2² = 66721842787 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 (66721842793) 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, 219995 + ... + 426428.

It is an arithmetic number, because the mean of its divisors is an integer number (16680648108).

Almost surely, 2^66721842791 is an apocalyptic number.

66721842791 is a deficient number, since it is larger than the sum of its proper divisors (749641).

66721842791 is a wasteful number, since it uses less digits than its factorization.

66721842791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 749640.

The product of its digits is 2032128, while the sum is 53.

The spelling of 66721842791 in words is "sixty-six billion, seven hundred twenty-one million, eight hundred forty-two thousand, seven hundred ninety-one".