66681699984 has 135 divisors (see below), whose sum is σ = 194027291497. Its totient is φ = 22199344704.

The previous prime is 66681699971. The next prime is 66681699989. The reversal of 66681699984 is 48999618666.

The square root of 66681699984 is 258228.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 32335232400 + 34346467584 = 179820^2 + 185328^2 .

It is a super-2 number, since 2×66681699984² (a number of 22 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (72).

It is a nude number because it is divisible by every one of its digits.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66681699989) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 83665474 + ... + 83666270.

Almost surely, 2^66681699984 is an apocalyptic number.

66681699984 is the 258228-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 66681699984

66681699984 is an abundant number, since it is smaller than the sum of its proper divisors (127345591513).

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

66681699984 is an frugal number, since it uses more digits than its factorization.

66681699984 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1626 (or 802 counting only the distinct ones).

The product of its digits is 241864704, while the sum is 72.

The spelling of 66681699984 in words is "sixty-six billion, six hundred eighty-one million, six hundred ninety-nine thousand, nine hundred eighty-four".