660565721 has 4 divisors (see below), whose sum is σ = 661890000. Its totient is φ = 659241444.

The previous prime is 660565691. The next prime is 660565729. The reversal of 660565721 is 127565066.

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 660565721 - 2¹⁸ = 660303577 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (660565729) 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, 661391 + ... + 662388.

It is an arithmetic number, because the mean of its divisors is an integer number (165472500).

Almost surely, 2^660565721 is an apocalyptic number.

It is an amenable number.

660565721 is a deficient number, since it is larger than the sum of its proper divisors (1324279).

660565721 is a wasteful number, since it uses less digits than its factorization.

660565721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1324278.

The product of its (nonzero) digits is 75600, while the sum is 38.

The square root of 660565721 is about 25701.4731289862. The cubic root of 660565721 is about 870.9074606761.

The spelling of 660565721 in words is "six hundred sixty million, five hundred sixty-five thousand, seven hundred twenty-one".