66561280 has 72 divisors (see below), whose sum is σ = 160965000. Its totient is φ = 26370048.

The previous prime is 66561277. The next prime is 66561281. The reversal of 66561280 is 8216566.

66561280 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 3326976 + 63234304 = 1824^2 + 7952^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66561281) 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 7 ways as a sum of consecutive naturals, for example, 190546 + ... + 190894.

It is an arithmetic number, because the mean of its divisors is an integer number (2235625).

Almost surely, 2^66561280 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 66561280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (80482500).

66561280 is an abundant number, since it is smaller than the sum of its proper divisors (94403720).

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

66561280 is a wasteful number, since it uses less digits than its factorization.

66561280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 519 (or 505 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 34.

The square root of 66561280 is about 8158.5096678254. The cubic root of 66561280 is about 405.2663593560.

The spelling of 66561280 in words is "sixty-six million, five hundred sixty-one thousand, two hundred eighty".