999999391 has 2 divisors, whose sum is σ = 999999392. Its totient is φ = 999999390.

The previous prime is 999999353. The next prime is 999999433. The reversal of 999999391 is 193999999.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 999999391 - 2²³ = 991610783 is a prime.

It is a super-3 number, since 3×999999391³ (a number of 28 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999999191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499999695 + 499999696.

It is an arithmetic number, because the mean of its divisors is an integer number (499999696).

Almost surely, 2^999999391 is an apocalyptic number.

999999391 is a deficient number, since it is larger than the sum of its proper divisors (1).

999999391 is an equidigital number, since it uses as much as digits as its factorization.

999999391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14348907, while the sum is 67.

The square root of 999999391 is about 31622.7669725469. The cubic root of 999999391 is about 999.9997970000. Note that the first 3 decimals are identical.

The spelling of 999999391 in words is "nine hundred ninety-nine million, nine hundred ninety-nine thousand, three hundred ninety-one".