9861991 has 2 divisors, whose sum is σ = 9861992. Its totient is φ = 9861990.

The previous prime is 9861983. The next prime is 9862019. The reversal of 9861991 is 1991689.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 9861991 - 2³ = 9861983 is a prime.

9861991 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9861191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4930995 + 4930996.

It is an arithmetic number, because the mean of its divisors is an integer number (4930996).

Almost surely, 2^9861991 is an apocalyptic number.

9861991 is a deficient number, since it is larger than the sum of its proper divisors (1).

9861991 is an equidigital number, since it uses as much as digits as its factorization.

9861991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 34992, while the sum is 43.

The square root of 9861991 is about 3140.3807094045. The cubic root of 9861991 is about 214.4477697519.

The spelling of 9861991 in words is "nine million, eight hundred sixty-one thousand, nine hundred ninety-one".