1661889991 has 2 divisors, whose sum is σ = 1661889992. Its totient is φ = 1661889990.

The previous prime is 1661889959. The next prime is 1661890033. The reversal of 1661889991 is 1999881661.

It is a happy number.

It is a weak prime.

It is an emirp because it is prime and its reverse (1999881661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1661889991 - 2⁵ = 1661889959 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1661889091) 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, 830944995 + 830944996.

It is an arithmetic number, because the mean of its divisors is an integer number (830944996).

Almost surely, 2^1661889991 is an apocalyptic number.

1661889991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661889991 is an equidigital number, since it uses as much as digits as its factorization.

1661889991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1679616, while the sum is 58.

The square root of 1661889991 is about 40766.2849791344. The cubic root of 1661889991 is about 1184.4973426398.

The spelling of 1661889991 in words is "one billion, six hundred sixty-one million, eight hundred eighty-nine thousand, nine hundred ninety-one".