999997891 has 2 divisors, whose sum is σ = 999997892. Its totient is φ = 999997890.

The previous prime is 999997871. The next prime is 999997967. The reversal of 999997891 is 198799999.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-999997891 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 999997891.

It is not a weakly prime, because it can be changed into another prime (999997811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499998945 + 499998946.

It is an arithmetic number, because the mean of its divisors is an integer number (499998946).

Almost surely, 2^999997891 is an apocalyptic number.

999997891 is a deficient number, since it is larger than the sum of its proper divisors (1).

999997891 is an equidigital number, since it uses as much as digits as its factorization.

999997891 is an evil number, because the sum of its binary digits is even.

The product of its digits is 29760696, while the sum is 70.

The square root of 999997891 is about 31622.7432554483. The cubic root of 999997891 is about 999.9992969995. Note that the first 3 decimals are identical.

The spelling of 999997891 in words is "nine hundred ninety-nine million, nine hundred ninety-seven thousand, eight hundred ninety-one".