16401991 has 4 divisors (see below), whose sum is σ = 17366832. Its totient is φ = 15437152.

The previous prime is 16401977. The next prime is 16402003. The reversal of 16401991 is 19910461.

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 16401991 - 2²¹ = 14304839 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 (16401911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 482395 + ... + 482428.

It is an arithmetic number, because the mean of its divisors is an integer number (4341708).

Almost surely, 2^16401991 is an apocalyptic number.

16401991 is a deficient number, since it is larger than the sum of its proper divisors (964841).

16401991 is an equidigital number, since it uses as much as digits as its factorization.

16401991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 964840.

The product of its (nonzero) digits is 1944, while the sum is 31.

The square root of 16401991 is about 4049.9371600063. The cubic root of 16401991 is about 254.0770995823.

The spelling of 16401991 in words is "sixteen million, four hundred one thousand, nine hundred ninety-one".