1999861 has 4 divisors (see below), whose sum is σ = 2004300. Its totient is φ = 1995424.

The previous prime is 1999859. The next prime is 1999867. The reversal of 1999861 is 1689991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1689991 = 1297 ⋅1303.

It can be written as a sum of positive squares in 2 ways, for example, as 938961 + 1060900 = 969^2 + 1030^2 .

It is a cyclic number.

It is not a de Polignac number, because 1999861 - 2¹ = 1999859 is a prime.

It is a Duffinian number.

1999861 is a lucky number.

It is a zygodrome in base 7.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1999867) 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, 1456 + ... + 2473.

It is an arithmetic number, because the mean of its divisors is an integer number (501075).

2^1999861 is an apocalyptic number.

It is an amenable number.

1999861 is a deficient number, since it is larger than the sum of its proper divisors (4439).

1999861 is an equidigital number, since it uses as much as digits as its factorization.

1999861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4438.

The product of its digits is 34992, while the sum is 43.

The square root of 1999861 is about 1414.1644175979. The cubic root of 1999861 is about 125.9891861048.

The spelling of 1999861 in words is "one million, nine hundred ninety-nine thousand, eight hundred sixty-one".