1981618 has 4 divisors (see below), whose sum is σ = 2972430. Its totient is φ = 990808.

The previous prime is 1981607. The next prime is 1981619. The reversal of 1981618 is 8161891.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 8161891 = 1181 ⋅6911.

It can be written as a sum of positive squares in only one way, i.e., 1046529 + 935089 = 1023^2 + 967^2 .

It is not an unprimeable number, because it can be changed into a prime (1981619) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495403 + ... + 495406.

2^1981618 is an apocalyptic number.

1981618 is a deficient number, since it is larger than the sum of its proper divisors (990812).

1981618 is an equidigital number, since it uses as much as digits as its factorization.

1981618 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 990811.

The product of its digits is 3456, while the sum is 34.

The square root of 1981618 is about 1407.6995418057. The cubic root of 1981618 is about 125.6049185330.

The spelling of 1981618 in words is "one million, nine hundred eighty-one thousand, six hundred eighteen".