66544640 has 88 divisors (see below), whose sum is σ = 164038392. Its totient is φ = 25886720.

The previous prime is 66544637. The next prime is 66544649. The reversal of 66544640 is 4644566.

It can be written as a sum of positive squares in 4 ways, for example, as 3564544 + 62980096 = 1888^2 + 7936^2 .

It is a super-2 number, since 2×66544640² = 8856378225459200, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 66544640.

It is not an unprimeable number, because it can be changed into a prime (66544649) 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, 209762 + ... + 210078.

Almost surely, 2^66544640 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 66544640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (82019196).

66544640 is an abundant number, since it is smaller than the sum of its proper divisors (97493752).

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

66544640 is a wasteful number, since it uses less digits than its factorization.

66544640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 383 (or 365 counting only the distinct ones).

The product of its (nonzero) digits is 69120, while the sum is 35.

The square root of 66544640 is about 8157.4898099844. The cubic root of 66544640 is about 405.2325849943.

The spelling of 66544640 in words is "sixty-six million, five hundred forty-four thousand, six hundred forty".