401991 has 8 divisors (see below), whose sum is σ = 547584. Its totient is φ = 262200.

The previous prime is 401987. The next prime is 401993. The reversal of 401991 is 199104.

401991 = 13² + 14² + ... + 106².

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 401991 - 2² = 401987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (401993) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1285 + ... + 1566.

It is an arithmetic number, because the mean of its divisors is an integer number (68448).

2⁴⁰¹⁹⁹¹ is an apocalyptic number.

401991 is a deficient number, since it is larger than the sum of its proper divisors (145593).

401991 is a wasteful number, since it uses less digits than its factorization.

401991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2901.

The product of its (nonzero) digits is 324, while the sum is 24.

The square root of 401991 is about 634.0276019228. The cubic root of 401991 is about 73.8026761465.

The spelling of 401991 in words is "four hundred one thousand, nine hundred ninety-one".