1666681 has 3 divisors (see below), whose sum is σ = 1667973.
Its totient is φ = 1665390.
The previous prime is 1666657. The next prime is 1666711. The reversal of 1666681 is 1866661.
The square root of 1666681 is 1291.
It is a perfect power (a square), and thus also a powerful number.
It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.
It is not a de Polignac number, because 1666681 - 211 = 1664633 is a prime.
It is a super-2 number, since 2×16666812 = 5555651111522, which contains 22 as substring.
It is a Duffinian number.
It is not an unprimeable number, because it can be changed into a prime (1666081) 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 2 ways as a sum of consecutive naturals, for example, 646 + ... + 1936.
It is an arithmetic number, because the mean of its divisors is an integer number (555991).
21666681 is an apocalyptic number.
1666681 is the 1291-st square number.
1666681 is the 817-th centered pentagonal number and also the 646-th centered octagonal number.
It is an amenable number.
1666681 is a deficient number, since it is larger than the sum of its proper divisors (1292).
1666681 is an frugal number, since it uses more digits than its factorization.
1666681 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 2582 (or 1291 counting only the distinct ones).
The product of its digits is 10368, while the sum is 34.
The cubic root of 1666681 is about 118.5634500296.
The spelling of 1666681 in words is "one million, six hundred sixty-six thousand, six hundred eighty-one".