1991943787 has 2 divisors, whose sum is σ = 1991943788. Its totient is φ = 1991943786.

The previous prime is 1991943763. The next prime is 1991943817. The reversal of 1991943787 is 7873491991.

It is a weak prime.

It is an emirp because it is prime and its reverse (7873491991) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1991943787 is a prime.

It is not a weakly prime, because it can be changed into another prime (1991943587) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995971893 + 995971894.

It is an arithmetic number, because the mean of its divisors is an integer number (995971894).

Almost surely, 2^1991943787 is an apocalyptic number.

1991943787 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991943787 is an equidigital number, since it uses as much as digits as its factorization.

1991943787 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3429216, while the sum is 58.

The square root of 1991943787 is about 44631.1974632095. The cubic root of 1991943787 is about 1258.2270746270.

The spelling of 1991943787 in words is "one billion, nine hundred ninety-one million, nine hundred forty-three thousand, seven hundred eighty-seven".