1671991 has 4 divisors (see below), whose sum is σ = 1703592. Its totient is φ = 1640392.

The previous prime is 1671983. The next prime is 1671997. The reversal of 1671991 is 1991761.

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 1671991 - 2³ = 1671983 is a prime.

It is a Duffinian number.

1671991 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1671997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15721 + ... + 15826.

It is an arithmetic number, because the mean of its divisors is an integer number (425898).

2^1671991 is an apocalyptic number.

1671991 is a deficient number, since it is larger than the sum of its proper divisors (31601).

1671991 is an equidigital number, since it uses as much as digits as its factorization.

1671991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31600.

The product of its digits is 3402, while the sum is 34.

The square root of 1671991 is about 1293.0549098936. The cubic root of 1671991 is about 118.6892298481.

It can be divided in two parts, 1671 and 991, that added together give a palindrome (2662).

The spelling of 1671991 in words is "one million, six hundred seventy-one thousand, nine hundred ninety-one".