661766327821 has 4 divisors (see below), whose sum is σ = 669739416192. Its totient is φ = 653793239452.

The previous prime is 661766327819. The next prime is 661766327903. The reversal of 661766327821 is 128723667166.

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 661766327821 - 2¹ = 661766327819 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 (661766322821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3986544061 + ... + 3986544226.

It is an arithmetic number, because the mean of its divisors is an integer number (167434854048).

Almost surely, 2^661766327821 is an apocalyptic number.

It is an amenable number.

661766327821 is a deficient number, since it is larger than the sum of its proper divisors (7973088371).

661766327821 is an equidigital number, since it uses as much as digits as its factorization.

661766327821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7973088370.

The product of its digits is 6096384, while the sum is 55.

The spelling of 661766327821 in words is "six hundred sixty-one billion, seven hundred sixty-six million, three hundred twenty-seven thousand, eight hundred twenty-one".