661605001 has 4 divisors (see below), whose sum is σ = 662318100. Its totient is φ = 660891904.

The previous prime is 661604981. The next prime is 661605011. The reversal of 661605001 is 100506166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 100506166 = 2 ⋅50253083.

It can be written as a sum of positive squares in 2 ways, for example, as 6245001 + 655360000 = 2499^2 + 25600^2 .

It is a cyclic number.

It is not a de Polignac number, because 661605001 - 2⁵ = 661604969 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661605011) 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, 355156 + ... + 357013.

It is an arithmetic number, because the mean of its divisors is an integer number (165579525).

Almost surely, 2^661605001 is an apocalyptic number.

It is an amenable number.

661605001 is a deficient number, since it is larger than the sum of its proper divisors (713099).

661605001 is an equidigital number, since it uses as much as digits as its factorization.

661605001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 713098.

The product of its (nonzero) digits is 1080, while the sum is 25.

The square root of 661605001 is about 25721.6834791193. The cubic root of 661605001 is about 871.3639595086.

The spelling of 661605001 in words is "six hundred sixty-one million, six hundred five thousand, one".