1998661 has 8 divisors (see below), whose sum is σ = 2331200. Its totient is φ = 1712844.

The previous prime is 1998643. The next prime is 1998679. The reversal of 1998661 is 1668991.

It is an interprime number because it is at equal distance from previous prime (1998643) and next prime (1998679).

It is not a de Polignac number, because 1998661 - 2⁷ = 1998533 is a prime.

1998661 is a strobogrammatic number because it is the same when read upside-down.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1998611) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2571 + ... + 3256.

It is an arithmetic number, because the mean of its divisors is an integer number (291400).

2^1998661 is an apocalyptic number.

It is an amenable number.

1998661 is a deficient number, since it is larger than the sum of its proper divisors (332539).

1998661 is an frugal number, since it uses more digits than its factorization.

1998661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5848 (or 5834 counting only the distinct ones).

The product of its digits is 23328, while the sum is 40.

The square root of 1998661 is about 1413.7400751199. The cubic root of 1998661 is about 125.9639814742.

The spelling of 1998661 in words is "one million, nine hundred ninety-eight thousand, six hundred sixty-one".