1998781 has 4 divisors (see below), whose sum is σ = 2104000. Its totient is φ = 1893564.

The previous prime is 1998761. The next prime is 1998793. The reversal of 1998781 is 1878991.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1998781 - 2¹⁷ = 1867709 is a prime.

It is a super-2 number, since 2×1998781² = 7990250971922, which contains 22 as substring.

It is a Duffinian number.

1998781 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1998701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 52581 + ... + 52618.

It is an arithmetic number, because the mean of its divisors is an integer number (526000).

2^1998781 is an apocalyptic number.

It is an amenable number.

1998781 is a deficient number, since it is larger than the sum of its proper divisors (105219).

1998781 is a wasteful number, since it uses less digits than its factorization.

1998781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 105218.

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

The square root of 1998781 is about 1413.7825150991. The cubic root of 1998781 is about 125.9665023912.

The spelling of 1998781 in words is "one million, nine hundred ninety-eight thousand, seven hundred eighty-one".