991661 has 8 divisors (see below), whose sum is σ = 1145664. Its totient is φ = 848320.

The previous prime is 991651. The next prime is 991663. The reversal of 991661 is 166199.

991661 = 154² + 155² + ... + 187².

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 991661 - 2¹⁰ = 990637 is a prime.

It is a Curzon number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991661.

It is not an unprimeable number, because it can be changed into a prime (991663) 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 7 ways as a sum of consecutive naturals, for example, 2465 + ... + 2838.

It is an arithmetic number, because the mean of its divisors is an integer number (143208).

2⁹⁹¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

991661 is a deficient number, since it is larger than the sum of its proper divisors (154003).

991661 is a wasteful number, since it uses less digits than its factorization.

991661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5331.

The product of its digits is 2916, while the sum is 32.

The square root of 991661 is about 995.8217712021. The cubic root of 991661 is about 99.7212570791.

The spelling of 991661 in words is "nine hundred ninety-one thousand, six hundred sixty-one".