1661115991 has 2 divisors, whose sum is σ = 1661115992. Its totient is φ = 1661115990.

The previous prime is 1661115977. The next prime is 1661116001. The reversal of 1661115991 is 1995111661.

It is a strong prime.

It is an emirp because it is prime and its reverse (1995111661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1661115991 - 2⁹ = 1661115479 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1661115091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830557995 + 830557996.

It is an arithmetic number, because the mean of its divisors is an integer number (830557996).

Almost surely, 2^1661115991 is an apocalyptic number.

1661115991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661115991 is an equidigital number, since it uses as much as digits as its factorization.

1661115991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 14580, while the sum is 40.

The square root of 1661115991 is about 40756.7907347966. The cubic root of 1661115991 is about 1184.3134268744.

The spelling of 1661115991 in words is "one billion, six hundred sixty-one million, one hundred fifteen thousand, nine hundred ninety-one".