1781998 has 4 divisors (see below), whose sum is σ = 2673000. Its totient is φ = 890998.

The previous prime is 1781981. The next prime is 1782043. The reversal of 1781998 is 8991871.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 8991871 = 7 ⋅1284553.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 445498 + ... + 445501.

It is an arithmetic number, because the mean of its divisors is an integer number (668250).

2^1781998 is an apocalyptic number.

1781998 is a deficient number, since it is larger than the sum of its proper divisors (891002).

1781998 is an equidigital number, since it uses as much as digits as its factorization.

1781998 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 891001.

The product of its digits is 36288, while the sum is 43.

The square root of 1781998 is about 1334.9149785661. The cubic root of 1781998 is about 121.2371552624.

The spelling of 1781998 in words is "one million, seven hundred eighty-one thousand, nine hundred ninety-eight".