661328191 has 2 divisors, whose sum is σ = 661328192. Its totient is φ = 661328190.

The previous prime is 661328189. The next prime is 661328201. The reversal of 661328191 is 191823166.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 661328191 - 2¹ = 661328189 is a prime.

It is a super-2 number, since 2×661328191² = 874709952422664962, which contains 22 as substring.

Together with 661328189, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 661328191.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661328891) 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 as a sum of consecutive naturals, namely, 330664095 + 330664096.

It is an arithmetic number, because the mean of its divisors is an integer number (330664096).

Almost surely, 2^661328191 is an apocalyptic number.

661328191 is a deficient number, since it is larger than the sum of its proper divisors (1).

661328191 is an equidigital number, since it uses as much as digits as its factorization.

661328191 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15552, while the sum is 37.

The square root of 661328191 is about 25716.3020475340. The cubic root of 661328191 is about 871.2424187584.

The spelling of 661328191 in words is "six hundred sixty-one million, three hundred twenty-eight thousand, one hundred ninety-one".