1666561321 has 8 divisors (see below), whose sum is σ = 1684255040. Its totient is φ = 1648896912.

The previous prime is 1666561249. The next prime is 1666561331. The reversal of 1666561321 is 1231656661.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1666561321 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1666561331) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 118270 + ... + 131608.

It is an arithmetic number, because the mean of its divisors is an integer number (210531880).

Almost surely, 2^1666561321 is an apocalyptic number.

It is an amenable number.

1666561321 is a deficient number, since it is larger than the sum of its proper divisors (17693719).

1666561321 is a wasteful number, since it uses less digits than its factorization.

1666561321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14655.

The product of its digits is 38880, while the sum is 37.

The square root of 1666561321 is about 40823.5388103481. The cubic root of 1666561321 is about 1185.6061207506.

The spelling of 1666561321 in words is "one billion, six hundred sixty-six million, five hundred sixty-one thousand, three hundred twenty-one".