1661881 has 4 divisors (see below), whose sum is σ = 1789732. Its totient is φ = 1534032.

The previous prime is 1661861. The next prime is 1661887. The reversal of 1661881 is 1881661.

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: 1881661 = 277 ⋅6793.

It can be written as a sum of positive squares in 2 ways, for example, as 360000 + 1301881 = 600^2 + 1141^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661881 - 2¹³ = 1653689 is a prime.

It is a super-2 number, since 2×1661881² = 5523696916322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1661887) 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, 63906 + ... + 63931.

It is an arithmetic number, because the mean of its divisors is an integer number (447433).

2^1661881 is an apocalyptic number.

It is an amenable number.

1661881 is a deficient number, since it is larger than the sum of its proper divisors (127851).

1661881 is a wasteful number, since it uses less digits than its factorization.

1661881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 127850.

The product of its digits is 2304, while the sum is 31.

The square root of 1661881 is about 1289.1396355709. The cubic root of 1661881 is about 118.4495206551.

The spelling of 1661881 in words is "one million, six hundred sixty-one thousand, eight hundred eighty-one".