399999999991 has 4 divisors (see below), whose sum is σ = 400002449184. Its totient is φ = 399997550800.

The previous prime is 399999999977. The next prime is 400000000019. The reversal of 399999999991 is 199999999993.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199999999993 = 31 ⋅6451612903.

It is a cyclic number.

It is not a de Polignac number, because 399999999991 - 2⁹ = 399999999479 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 399999999991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (399999999911) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 960655 + ... + 1312576.

It is an arithmetic number, because the mean of its divisors is an integer number (100000612296).

Almost surely, 2^399999999991 is an apocalyptic number.

399999999991 is a deficient number, since it is larger than the sum of its proper divisors (2449193).

399999999991 is a wasteful number, since it uses less digits than its factorization.

399999999991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2449192.

The product of its digits is 10460353203, while the sum is 94.

It can be divided in two parts, 39999999999 and 1, that added together give a square (40000000000 = 200000²).

The spelling of 399999999991 in words is "three hundred ninety-nine billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred ninety-one".