661998 has 16 divisors (see below), whose sum is σ = 1393920. Its totient is φ = 209016.

The previous prime is 661993. The next prime is 662003. The reversal of 661998 is 899166.

It is an interprime number because it is at equal distance from previous prime (661993) and next prime (662003).

It is a Curzon number.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661993) by changing a digit.

661998 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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 7 ways as a sum of consecutive naturals, for example, 2790 + ... + 3017.

It is an arithmetic number, because the mean of its divisors is an integer number (87120).

2⁶⁶¹⁹⁹⁸ is an apocalyptic number.

661998 is an abundant number, since it is smaller than the sum of its proper divisors (731922).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

661998 is a wasteful number, since it uses less digits than its factorization.

661998 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5831.

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

The square root of 661998 is about 813.6325952173. The cubic root of 661998 is about 87.1536457893.

The spelling of 661998 in words is "six hundred sixty-one thousand, nine hundred ninety-eight".