1666381 has 4 divisors (see below), whose sum is σ = 1669564. Its totient is φ = 1663200.

The previous prime is 1666361. The next prime is 1666387. The reversal of 1666381 is 1836661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1836661 = 241 ⋅7621.

It can be written as a sum of positive squares in 2 ways, for example, as 476100 + 1190281 = 690^2 + 1091^2 .

It is a cyclic number.

It is not a de Polignac number, because 1666381 - 2⁹ = 1665869 is a prime.

It is a super-2 number, since 2×1666381² = 5553651274322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1666387) 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, 600 + ... + 1921.

It is an arithmetic number, because the mean of its divisors is an integer number (417391).

2^1666381 is an apocalyptic number.

It is an amenable number.

1666381 is a deficient number, since it is larger than the sum of its proper divisors (3183).

1666381 is an equidigital number, since it uses as much as digits as its factorization.

1666381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3182.

The product of its digits is 5184, while the sum is 31.

The square root of 1666381 is about 1290.8838057703. The cubic root of 1666381 is about 118.5563358569.

The spelling of 1666381 in words is "one million, six hundred sixty-six thousand, three hundred eighty-one".