1591991 has 8 divisors (see below), whose sum is σ = 1749120. Its totient is φ = 1442232.

The previous prime is 1591981. The next prime is 1592027. The reversal of 1591991 is 1991951.

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

It is a cyclic number.

It is not a de Polignac number, because 1591991 - 2⁶ = 1591927 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 (1591901) 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 7 ways as a sum of consecutive naturals, for example, 1385 + ... + 2258.

It is an arithmetic number, because the mean of its divisors is an integer number (218640).

2^1591991 is an apocalyptic number.

1591991 is a deficient number, since it is larger than the sum of its proper divisors (157129).

1591991 is a wasteful number, since it uses less digits than its factorization.

1591991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3685.

The product of its digits is 3645, while the sum is 35.

The square root of 1591991 is about 1261.7412571522. The cubic root of 1591991 is about 116.7652291805.

The spelling of 1591991 in words is "one million, five hundred ninety-one thousand, nine hundred ninety-one".