400003991 has 4 divisors (see below), whose sum is σ = 400044000. Its totient is φ = 399963984.

The previous prime is 400003987. The next prime is 400003993. The reversal of 400003991 is 199300004.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 400003991 - 2² = 400003987 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 400003991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (400003993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9410 + ... + 29808.

It is an arithmetic number, because the mean of its divisors is an integer number (100011000).

Almost surely, 2^400003991 is an apocalyptic number.

400003991 is a deficient number, since it is larger than the sum of its proper divisors (40009).

400003991 is a wasteful number, since it uses less digits than its factorization.

400003991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40008.

The product of its (nonzero) digits is 972, while the sum is 26.

The square root of 400003991 is about 20000.0997747511. The cubic root of 400003991 is about 736.8087502149.

Adding to 400003991 its reverse (199300004), we get a palindrome (599303995).

The spelling of 400003991 in words is "four hundred million, three thousand, nine hundred ninety-one".