400991 has 4 divisors (see below), whose sum is σ = 404184. Its totient is φ = 397800.

The previous prime is 400963. The next prime is 400997. The reversal of 400991 is 199004.

400991 = T₃ + T₄ + ... + T₁₃₃.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 400991 - 2⁶ = 400927 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (400997) 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, 1400 + ... + 1661.

It is an arithmetic number, because the mean of its divisors is an integer number (101046).

2⁴⁰⁰⁹⁹¹ is an apocalyptic number.

400991 is a deficient number, since it is larger than the sum of its proper divisors (3193).

400991 is a wasteful number, since it uses less digits than its factorization.

400991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3192.

The product of its (nonzero) digits is 324, while the sum is 23.

The square root of 400991 is about 633.2385016722. The cubic root of 400991 is about 73.7414277119.

Adding to 400991 its reverse (199004), we get a palindrome (599995).

The spelling of 400991 in words is "four hundred thousand, nine hundred ninety-one".