9999991 has 2 divisors, whose sum is σ = 9999992. Its totient is φ = 9999990.

The previous prime is 9999973. The next prime is 10000019. The reversal of 9999991 is 1999999.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 9999991 - 2⁷ = 9999863 is a prime.

It is a Chen prime.

It is a nialpdrome in base 10.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9999901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4999995 + 4999996.

It is an arithmetic number, because the mean of its divisors is an integer number (4999996).

Almost surely, 2^9999991 is an apocalyptic number.

9999991 is a deficient number, since it is larger than the sum of its proper divisors (1).

9999991 is an equidigital number, since it uses as much as digits as its factorization.

9999991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 531441, while the sum is 55.

The square root of 9999991 is about 3162.2762371431. The cubic root of 9999991 is about 215.4434043701.

It can be divided in two parts, 999999 and 1, that added together give a 6-th power (1000000 = 10⁶).

The spelling of 9999991 in words is "nine million, nine hundred ninety-nine thousand, nine hundred ninety-one".