1666721200 has 120 divisors (see below), whose sum is σ = 4167511040. Its totient is φ = 639878400.

The previous prime is 1666721179. The next prime is 1666721207. The reversal of 1666721200 is 21276661.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is not an unprimeable number, because it can be changed into a prime (1666721207) 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 23 ways as a sum of consecutive naturals, for example, 1723117 + ... + 1724083.

Almost surely, 2^1666721200 is an apocalyptic number.

1666721200 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1666721200, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2083755520).

1666721200 is an abundant number, since it is smaller than the sum of its proper divisors (2500789840).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1666721200 is a wasteful number, since it uses less digits than its factorization.

1666721200 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1155 (or 1144 counting only the distinct ones).

The product of its (nonzero) digits is 6048, while the sum is 31.

The square root of 1666721200 is about 40825.4969351262. The cubic root of 1666721200 is about 1185.6440326389.

Adding to 1666721200 its reverse (21276661), we get a palindrome (1687997861).

The spelling of 1666721200 in words is "one billion, six hundred sixty-six million, seven hundred twenty-one thousand, two hundred".