561866 has 4 divisors (see below), whose sum is σ = 842802. Its totient is φ = 280932.

The previous prime is 561839. The next prime is 561907. The reversal of 561866 is 668165.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 668165 = 5 ⋅133633.

It can be written as a sum of positive squares in only one way, i.e., 519841 + 42025 = 721^2 + 205^2 .

It is an Ulam number.

It is an unprimeable number.

561866 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 140465 + ... + 140468.

2⁵⁶¹⁸⁶⁶ is an apocalyptic number.

561866 is a deficient number, since it is larger than the sum of its proper divisors (280936).

561866 is a wasteful number, since it uses less digits than its factorization.

561866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 280935.

The product of its digits is 8640, while the sum is 32.

The square root of 561866 is about 749.5772141681. The cubic root of 561866 is about 82.5171559057.

The spelling of 561866 in words is "five hundred sixty-one thousand, eight hundred sixty-six".