251866 has 4 divisors (see below), whose sum is σ = 377802. Its totient is φ = 125932.

The previous prime is 251861. The next prime is 251879. The reversal of 251866 is 668152.

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., 235225 + 16641 = 485^2 + 129^2 .

It is not an unprimeable number, because it can be changed into a prime (251861) 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 as a sum of consecutive naturals, namely, 62965 + ... + 62968.

2²⁵¹⁸⁶⁶ is an apocalyptic number.

251866 is a deficient number, since it is larger than the sum of its proper divisors (125936).

251866 is a wasteful number, since it uses less digits than its factorization.

251866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 125935.

The product of its digits is 2880, while the sum is 28.

The square root of 251866 is about 501.8625309784. The cubic root of 251866 is about 63.1523983277.

It can be divided in two parts, 25 and 1866, that added together give a triangular number (1891 = T₆₁).

The spelling of 251866 in words is "two hundred fifty-one thousand, eight hundred sixty-six".