1666 has 12 divisors (see below), whose sum is σ = 3078. Its totient is φ = 672.

The previous prime is 1663. The next prime is 1667. The reversal of 1666 is 6661.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 1225 + 441 = 35^2 + 21^2 .

1666 is a modest number, since divided by 66 gives 16 as remainder.

It is a plaindrome in base 10.

It is a nialpdrome in base 14 and base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1663) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 90 + ... + 106.

2¹⁶⁶⁶ is an apocalyptic number.

1666 is a deficient number, since it is larger than the sum of its proper divisors (1412).

1666 is a wasteful number, since it uses less digits than its factorization.

1666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33 (or 26 counting only the distinct ones).

The product of its digits is 216, while the sum is 19.

The square root of 1666 is about 40.8166632639. The cubic root of 1666 is about 11.8547299627.

The spelling of 1666 in words is "one thousand, six hundred sixty-six".