1666561 has 8 divisors (see below), whose sum is σ = 1900584. Its totient is φ = 1447680.

The previous prime is 1666559. The next prime is 1666589. The reversal of 1666561 is 1656661.

It can be written as a sum of positive squares in 4 ways, for example, as 25600 + 1640961 = 160^2 + 1281^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 1666561 - 2¹ = 1666559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1666531) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3550 + ... + 3991.

It is an arithmetic number, because the mean of its divisors is an integer number (237573).

2^1666561 is an apocalyptic number.

It is an amenable number.

1666561 is a deficient number, since it is larger than the sum of its proper divisors (234023).

1666561 is a wasteful number, since it uses less digits than its factorization.

1666561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7571.

The product of its digits is 6480, while the sum is 31.

The square root of 1666561 is about 1290.9535235631. The cubic root of 1666561 is about 118.5606044630.

The spelling of 1666561 in words is "one million, six hundred sixty-six thousand, five hundred sixty-one".