998661 has 4 divisors (see below), whose sum is σ = 1331552. Its totient is φ = 665772.

The previous prime is 998653. The next prime is 998681. The reversal of 998661 is 166899.

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, and also an emirpimes, since its reverse is a distinct semiprime: 166899 = 3 ⋅55633.

It is not a de Polignac number, because 998661 - 2³ = 998653 is a prime.

It is an Ulam number.

It is a D-number.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (998651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 166441 + ... + 166446.

It is an arithmetic number, because the mean of its divisors is an integer number (332888).

2⁹⁹⁸⁶⁶¹ is an apocalyptic number.

It is an amenable number.

998661 is a deficient number, since it is larger than the sum of its proper divisors (332891).

998661 is a wasteful number, since it uses less digits than its factorization.

998661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 332890.

The product of its digits is 23328, while the sum is 39.

The square root of 998661 is about 999.3302757347. The cubic root of 998661 is about 99.9553467305.

The spelling of 998661 in words is "nine hundred ninety-eight thousand, six hundred sixty-one".