991406591 has 4 divisors (see below), whose sum is σ = 1133036112. Its totient is φ = 849777072.

The previous prime is 991406573. The next prime is 991406597. The reversal of 991406591 is 195604199.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 991406591 - 2¹⁰ = 991405567 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 (991406597) 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, 70814750 + ... + 70814763.

It is an arithmetic number, because the mean of its divisors is an integer number (283259028).

Almost surely, 2^991406591 is an apocalyptic number.

991406591 is a deficient number, since it is larger than the sum of its proper divisors (141629521).

991406591 is a wasteful number, since it uses less digits than its factorization.

991406591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 141629520.

The product of its (nonzero) digits is 87480, while the sum is 44.

The square root of 991406591 is about 31486.6097095257. The cubic root of 991406591 is about 997.1272857485.

The spelling of 991406591 in words is "nine hundred ninety-one million, four hundred six thousand, five hundred ninety-one".