1666547721 has 24 divisors (see below), whose sum is σ = 2430704640. Its totient is φ = 1100234016.

The previous prime is 1666547719. The next prime is 1666547737. The reversal of 1666547721 is 1277456661.

It is not a de Polignac number, because 1666547721 - 2¹ = 1666547719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1666547711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 843691 + ... + 845663.

It is an arithmetic number, because the mean of its divisors is an integer number (101279360).

Almost surely, 2^1666547721 is an apocalyptic number.

It is an amenable number.

1666547721 is a deficient number, since it is larger than the sum of its proper divisors (764156919).

1666547721 is a wasteful number, since it uses less digits than its factorization.

1666547721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2845 (or 2842 counting only the distinct ones).

The product of its digits is 423360, while the sum is 45.

The square root of 1666547721 is about 40823.3722394415. The cubic root of 1666547721 is about 1185.6028956893.

The spelling of 1666547721 in words is "one billion, six hundred sixty-six million, five hundred forty-seven thousand, seven hundred twenty-one".