2001115561 has 4 divisors (see below), whose sum is σ = 2003020624. Its totient is φ = 1999210500.

The previous prime is 2001115517. The next prime is 2001115573. The reversal of 2001115561 is 1655111002.

It is a happy number.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1655111002 = 2 ⋅827555501.

It is a cyclic number.

It is not a de Polignac number, because 2001115561 - 2⁷ = 2001115433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2001115261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 950955 + ... + 953056.

It is an arithmetic number, because the mean of its divisors is an integer number (500755156).

Almost surely, 2^2001115561 is an apocalyptic number.

It is an amenable number.

2001115561 is a deficient number, since it is larger than the sum of its proper divisors (1905063).

2001115561 is a wasteful number, since it uses less digits than its factorization.

2001115561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1905062.

The product of its (nonzero) digits is 300, while the sum is 22.

The square root of 2001115561 is about 44733.8301624173. The cubic root of 2001115561 is about 1260.1552594855.

Adding to 2001115561 its reverse (1655111002), we get a palindrome (3656226563).

The spelling of 2001115561 in words is "two billion, one million, one hundred fifteen thousand, five hundred sixty-one".