66643640 has 64 divisors (see below), whose sum is σ = 180403200. Its totient is φ = 21644928.

The previous prime is 66643637. The next prime is 66643649. The reversal of 66643640 is 4634666.

It is a Harshad number since it is a multiple of its sum of digits (35).

It is a self number, because there is not a number n which added to its sum of digits gives 66643640.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66643649) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 944 + ... + 11583.

It is an arithmetic number, because the mean of its divisors is an integer number (2818800).

Almost surely, 2^66643640 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 66643640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (90201600).

66643640 is an abundant number, since it is smaller than the sum of its proper divisors (113759560).

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

66643640 is a wasteful number, since it uses less digits than its factorization.

66643640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12564 (or 12560 counting only the distinct ones).

The product of its (nonzero) digits is 62208, while the sum is 35.

The square root of 66643640 is about 8163.5555978997. Note that the first 4 decimals coincide. The cubic root of 66643640 is about 405.4334433830.

The spelling of 66643640 in words is "sixty-six million, six hundred forty-three thousand, six hundred forty".