660655621 has 4 divisors (see below), whose sum is σ = 669705772. Its totient is φ = 651605472.

The previous prime is 660655607. The next prime is 660655637. The reversal of 660655621 is 126556066.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 454158721 + 206496900 = 21311^2 + 14370^2 .

It is a cyclic number.

It is not a de Polignac number, because 660655621 - 2²¹ = 658558469 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (660655691) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4524966 + ... + 4525111.

It is an arithmetic number, because the mean of its divisors is an integer number (167426443).

Almost surely, 2^660655621 is an apocalyptic number.

It is an amenable number.

660655621 is a deficient number, since it is larger than the sum of its proper divisors (9050151).

660655621 is an equidigital number, since it uses as much as digits as its factorization.

660655621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9050150.

The product of its (nonzero) digits is 64800, while the sum is 37.

The square root of 660655621 is about 25703.2219964735. The cubic root of 660655621 is about 870.9469677363.

The spelling of 660655621 in words is "six hundred sixty million, six hundred fifty-five thousand, six hundred twenty-one".