666561600 has 252 divisors, whose sum is σ = 2429050260. Its totient is φ = 173260800.

The previous prime is 666561589. The next prime is 666561611. The reversal of 666561600 is 6165666.

666561600 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (666561589) and next prime (666561611).

It can be written as a sum of positive squares in 6 ways, for example, as 256256064 + 410305536 = 16008^2 + 20256^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 589836 + ... + 590964.

Almost surely, 2^666561600 is an apocalyptic number.

666561600 is a gapful number since it is divisible by the number (60) 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 666561600, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1214525130).

666561600 is an abundant number, since it is smaller than the sum of its proper divisors (1762488660).

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

666561600 is a wasteful number, since it uses less digits than its factorization.

666561600 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1198 (or 1180 counting only the distinct ones).

The product of its (nonzero) digits is 38880, while the sum is 36.

The square root of 666561600 is about 25817.8542872951. The cubic root of 666561600 is about 873.5345702315.

It can be divided in two parts, 6665 and 61600, that added together give a triangular number (68265 = T₃₆₉).

The spelling of 666561600 in words is "six hundred sixty-six million, five hundred sixty-one thousand, six hundred".