991109561 has 16 divisors (see below), whose sum is σ = 1079450064. Its totient is φ = 904560384.

The previous prime is 991109543. The next prime is 991109563. The reversal of 991109561 is 165901199.

991109561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 8 ways, for example, as 248220025 + 742889536 = 15755^2 + 27256^2 .

It is not a de Polignac number, because 991109561 - 2¹⁴ = 991093177 is a prime.

It is a super-2 number, since 2×991109561² = 1964596323811225442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991109563) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 441935 + ... + 444171.

It is an arithmetic number, because the mean of its divisors is an integer number (67465629).

Almost surely, 2^991109561 is an apocalyptic number.

It is an amenable number.

991109561 is a deficient number, since it is larger than the sum of its proper divisors (88340503).

991109561 is a wasteful number, since it uses less digits than its factorization.

991109561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2620.

The product of its (nonzero) digits is 21870, while the sum is 41.

The square root of 991109561 is about 31481.8925892329. The cubic root of 991109561 is about 997.0276944863.

The spelling of 991109561 in words is "nine hundred ninety-one million, one hundred nine thousand, five hundred sixty-one".