991657 has 4 divisors (see below), whose sum is σ = 1005696. Its totient is φ = 977620.

The previous prime is 991651. The next prime is 991663. The reversal of 991657 is 756199.

991657 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 an interprime number because it is at equal distance from previous prime (991651) and next prime (991663).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991657 is a prime.

It is a Duffinian number.

991657 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (991651) 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, 6913 + ... + 7054.

It is an arithmetic number, because the mean of its divisors is an integer number (251424).

2⁹⁹¹⁶⁵⁷ is an apocalyptic number.

It is an amenable number.

991657 is a deficient number, since it is larger than the sum of its proper divisors (14039).

991657 is a wasteful number, since it uses less digits than its factorization.

991657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14038.

The product of its digits is 17010, while the sum is 37.

The square root of 991657 is about 995.8197628085. The cubic root of 991657 is about 99.7211229991.

The spelling of 991657 in words is "nine hundred ninety-one thousand, six hundred fifty-seven".