191999987 has 2 divisors, whose sum is σ = 191999988. Its totient is φ = 191999986.

The previous prime is 191999971. The next prime is 192000043. The reversal of 191999987 is 789999191.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 191999987 - 2⁴ = 191999971 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (191999917) 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, 95999993 + 95999994.

It is an arithmetic number, because the mean of its divisors is an integer number (95999994).

Almost surely, 2^191999987 is an apocalyptic number.

191999987 is a deficient number, since it is larger than the sum of its proper divisors (1).

191999987 is an equidigital number, since it uses as much as digits as its factorization.

191999987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3306744, while the sum is 62.

The square root of 191999987 is about 13856.4059914539. The cubic root of 191999987 is about 576.8998151027.

The spelling of 191999987 in words is "one hundred ninety-one million, nine hundred ninety-nine thousand, nine hundred eighty-seven".