991557 has 12 divisors (see below), whose sum is σ = 1636960. Its totient is φ = 566568.

The previous prime is 991547. The next prime is 991567. The reversal of 991557 is 755199.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (991547) and next prime (991567).

It is not a de Polignac number, because 991557 - 2⁴ = 991541 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991547) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 7807 + ... + 7932.

2⁹⁹¹⁵⁵⁷ is an apocalyptic number.

It is an amenable number.

991557 is a deficient number, since it is larger than the sum of its proper divisors (645403).

991557 is a wasteful number, since it uses less digits than its factorization.

991557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15752 (or 15749 counting only the distinct ones).

The product of its digits is 14175, while the sum is 36.

The square root of 991557 is about 995.7695516534. The cubic root of 991557 is about 99.7177708833.

The spelling of 991557 in words is "nine hundred ninety-one thousand, five hundred fifty-seven".