661111561 has 4 divisors (see below), whose sum is σ = 721212624. Its totient is φ = 601010500.

The previous prime is 661111553. The next prime is 661111571. The reversal of 661111561 is 165111166.

661111561 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 a cyclic number.

It is not a de Polignac number, because 661111561 - 2³ = 661111553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661111501) 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, 30050515 + ... + 30050536.

It is an arithmetic number, because the mean of its divisors is an integer number (180303156).

Almost surely, 2^661111561 is an apocalyptic number.

It is an amenable number.

661111561 is a deficient number, since it is larger than the sum of its proper divisors (60101063).

661111561 is a wasteful number, since it uses less digits than its factorization.

661111561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 60101062.

The product of its digits is 1080, while the sum is 28.

The square root of 661111561 is about 25712.0897828240. The cubic root of 661111561 is about 871.1472779697.

The spelling of 661111561 in words is "six hundred sixty-one million, one hundred eleven thousand, five hundred sixty-one".