278665 has 4 divisors (see below), whose sum is σ = 334404. Its totient is φ = 222928.

The previous prime is 278651. The next prime is 278671. The reversal of 278665 is 566872.

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

It can be written as a sum of positive squares in 2 ways, for example, as 183184 + 95481 = 428^2 + 309^2 .

It is a cyclic number.

It is not a de Polignac number, because 278665 - 2¹⁵ = 245897 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 278665.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27862 + ... + 27871.

It is an arithmetic number, because the mean of its divisors is an integer number (83601).

2²⁷⁸⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

278665 is a deficient number, since it is larger than the sum of its proper divisors (55739).

278665 is an equidigital number, since it uses as much as digits as its factorization.

278665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55738.

The product of its digits is 20160, while the sum is 34.

The square root of 278665 is about 527.8872985780. The cubic root of 278665 is about 65.3171873424.

Subtracting from 278665 its sum of digits (34), we obtain a triangular number (278631 = T₇₄₆).

The spelling of 278665 in words is "two hundred seventy-eight thousand, six hundred sixty-five".