661006665 has 144 divisors (see below), whose sum is σ = 1376588304. Its totient is φ = 291962880.

The previous prime is 661006651. The next prime is 661006673. The reversal of 661006665 is 566600166.

It can be written as a sum of positive squares in 8 ways, for example, as 18688329 + 642318336 = 4323^2 + 25344^2 .

It is not a de Polignac number, because 661006665 - 2⁶ = 661006601 is a prime.

It is a super-2 number, since 2×661006665² = 873859622348844450, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 3424809 + ... + 3425001.

It is an arithmetic number, because the mean of its divisors is an integer number (9559641).

Almost surely, 2^661006665 is an apocalyptic number.

It is an amenable number.

661006665 is an abundant number, since it is smaller than the sum of its proper divisors (715581639).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

661006665 is a wasteful number, since it uses less digits than its factorization.

661006665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 280 (or 266 counting only the distinct ones).

The product of its (nonzero) digits is 38880, while the sum is 36.

The square root of 661006665 is about 25710.0498832655. The cubic root of 661006665 is about 871.1012016827.

The spelling of 661006665 in words is "six hundred sixty-one million, six thousand, six hundred sixty-five".