1661278 has 4 divisors (see below), whose sum is σ = 2491920. Its totient is φ = 830638.

The previous prime is 1661273. The next prime is 1661281. The reversal of 1661278 is 8721661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 8721661 = 13 ⋅670897.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661273) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 415318 + ... + 415321.

It is an arithmetic number, because the mean of its divisors is an integer number (622980).

2^1661278 is an apocalyptic number.

1661278 is a deficient number, since it is larger than the sum of its proper divisors (830642).

1661278 is an equidigital number, since it uses as much as digits as its factorization.

1661278 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 830641.

The product of its digits is 4032, while the sum is 31.

The square root of 1661278 is about 1288.9057374378. The cubic root of 1661278 is about 118.4351927737.

It can be divided in two parts, 166 and 1278, that added together give a square (1444 = 38²).

The spelling of 1661278 in words is "one million, six hundred sixty-one thousand, two hundred seventy-eight".