1666778 has 4 divisors (see below), whose sum is σ = 2500170. Its totient is φ = 833388.

The previous prime is 1666771. The next prime is 1666781. The reversal of 1666778 is 8776661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 8776661 = 1409 ⋅6229.

It can be written as a sum of positive squares in only one way, i.e., 1399489 + 267289 = 1183^2 + 517^2 .

It is a plaindrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (1666771) 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, 416693 + ... + 416696.

2^1666778 is an apocalyptic number.

1666778 is a deficient number, since it is larger than the sum of its proper divisors (833392).

1666778 is an equidigital number, since it uses as much as digits as its factorization.

1666778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 833391.

The product of its digits is 84672, while the sum is 41.

The square root of 1666778 is about 1291.0375672303. The cubic root of 1666778 is about 118.5657500961.

The spelling of 1666778 in words is "one million, six hundred sixty-six thousand, seven hundred seventy-eight".