665511561 has 48 divisors (see below), whose sum is σ = 1133233920. Its totient is φ = 371036160.

The previous prime is 665511557. The next prime is 665511569. The reversal of 665511561 is 165115566.

It is not a de Polignac number, because 665511561 - 2² = 665511557 is a prime.

It is not an unprimeable number, because it can be changed into a prime (665511569) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 471625 + ... + 473033.

It is an arithmetic number, because the mean of its divisors is an integer number (23609040).

Almost surely, 2^665511561 is an apocalyptic number.

It is an amenable number.

665511561 is a deficient number, since it is larger than the sum of its proper divisors (467722359).

665511561 is a wasteful number, since it uses less digits than its factorization.

665511561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1806 (or 1803 counting only the distinct ones).

The product of its digits is 27000, while the sum is 36.

The square root of 665511561 is about 25797.5107520086. The cubic root of 665511561 is about 873.0756341851.

The spelling of 665511561 in words is "six hundred sixty-five million, five hundred eleven thousand, five hundred sixty-one".