661778 has 8 divisors (see below), whose sum is σ = 1069068. Its totient is φ = 305424.

The previous prime is 661777. The next prime is 661823. The reversal of 661778 is 877166.

661778 is nontrivially palindromic in base 7.

It can be written as a sum of positive squares in 2 ways, for example, as 635209 + 26569 = 797^2 + 163^2 .

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

It is not an unprimeable number, because it can be changed into a prime (661777) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12701 + ... + 12752.

2⁶⁶¹⁷⁷⁸ is an apocalyptic number.

661778 is a deficient number, since it is larger than the sum of its proper divisors (407290).

661778 is a wasteful number, since it uses less digits than its factorization.

661778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25468.

The product of its digits is 14112, while the sum is 35.

The square root of 661778 is about 813.4973878262. The cubic root of 661778 is about 87.1439902081.

The spelling of 661778 in words is "six hundred sixty-one thousand, seven hundred seventy-eight".