1998561 has 4 divisors (see below), whose sum is σ = 2664752. Its totient is φ = 1332372.

The previous prime is 1998559. The next prime is 1998569. The reversal of 1998561 is 1658991.

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 not a de Polignac number, because 1998561 - 2¹ = 1998559 is a prime.

It is a D-number.

It is a Duffinian number.

1998561 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (1998569) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 333091 + ... + 333096.

It is an arithmetic number, because the mean of its divisors is an integer number (666188).

2^1998561 is an apocalyptic number.

It is an amenable number.

1998561 is a deficient number, since it is larger than the sum of its proper divisors (666191).

1998561 is an equidigital number, since it uses as much as digits as its factorization.

1998561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 666190.

The product of its digits is 19440, while the sum is 39.

The square root of 1998561 is about 1413.7047074973. The cubic root of 1998561 is about 125.9618806330.

The spelling of 1998561 in words is "one million, nine hundred ninety-eight thousand, five hundred sixty-one".