1801661 has 4 divisors (see below), whose sum is σ = 1818300. Its totient is φ = 1785024.

The previous prime is 1801619. The next prime is 1801669. The reversal of 1801661 is 1661081.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1661081 = 103 ⋅16127.

It can be written as a sum of positive squares in 2 ways, for example, as 1464100 + 337561 = 1210^2 + 581^2 .

It is a cyclic number.

It is not a de Polignac number, because 1801661 - 2¹⁰ = 1800637 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1801669) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8156 + ... + 8373.

It is an arithmetic number, because the mean of its divisors is an integer number (454575).

2^1801661 is an apocalyptic number.

It is an amenable number.

1801661 is a deficient number, since it is larger than the sum of its proper divisors (16639).

1801661 is a wasteful number, since it uses less digits than its factorization.

1801661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16638.

The product of its (nonzero) digits is 288, while the sum is 23.

The square root of 1801661 is about 1342.2596619134. The cubic root of 1801661 is about 121.6814452138.

The spelling of 1801661 in words is "one million, eight hundred one thousand, six hundred sixty-one".