1601991 has 8 divisors (see below), whose sum is σ = 2373360. Its totient is φ = 1067976.

The previous prime is 1601969. The next prime is 1602011. The reversal of 1601991 is 1991061.

It is not a de Polignac number, because 1601991 - 2¹⁰ = 1600967 is a prime.

It is a super-3 number, since 3×1601991³ = 12333929746443855813, which contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 59333 = 1601991 / (1 + 6 + 0 + 1 + 9 + 9 + 1).

It is a zygodrome in base 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1601591) 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, 29640 + ... + 29693.

It is an arithmetic number, because the mean of its divisors is an integer number (296670).

2^1601991 is an apocalyptic number.

1601991 is a deficient number, since it is larger than the sum of its proper divisors (771369).

1601991 is an equidigital number, since it uses as much as digits as its factorization.

1601991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59342 (or 59336 counting only the distinct ones).

The product of its (nonzero) digits is 486, while the sum is 27.

The square root of 1601991 is about 1265.6978312378. The cubic root of 1601991 is about 117.0092037467.

It can be divided in two parts, 16019 and 91, that added together give a triangular number (16110 = T₁₇₉).

The spelling of 1601991 in words is "one million, six hundred one thousand, nine hundred ninety-one".