19781998 has 4 divisors (see below), whose sum is σ = 29673000. Its totient is φ = 9890998.

The previous prime is 19781989. The next prime is 19782011. The reversal of 19781998 is 89918791.

It is a semiprime because it is the product of two primes.

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, 4945498 + ... + 4945501.

It is an arithmetic number, because the mean of its divisors is an integer number (7418250).

Almost surely, 2^19781998 is an apocalyptic number.

19781998 is a deficient number, since it is larger than the sum of its proper divisors (9891002).

19781998 is an equidigital number, since it uses as much as digits as its factorization.

19781998 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9891001.

The product of its digits is 326592, while the sum is 52.

The square root of 19781998 is about 4447.6958079437. The cubic root of 19781998 is about 270.4519089535.

The spelling of 19781998 in words is "nineteen million, seven hundred eighty-one thousand, nine hundred ninety-eight".