2561666 has 4 divisors (see below), whose sum is σ = 3842502. Its totient is φ = 1280832.

The previous prime is 2561659. The next prime is 2561681. The reversal of 2561666 is 6661652.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 2418025 + 143641 = 1555^2 + 379^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 640415 + ... + 640418.

2^2561666 is an apocalyptic number.

2561666 is a deficient number, since it is larger than the sum of its proper divisors (1280836).

2561666 is a wasteful number, since it uses less digits than its factorization.

2561666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1280835.

The product of its digits is 12960, while the sum is 32.

The square root of 2561666 is about 1600.5205403243. The cubic root of 2561666 is about 136.8277445067.

The spelling of 2561666 in words is "two million, five hundred sixty-one thousand, six hundred sixty-six".