66561786 has 36 divisors (see below), whose sum is σ = 149395662. Its totient is φ = 21417312.

The previous prime is 66561773. The next prime is 66561787. The reversal of 66561786 is 68716566.

66561786 is a `hidden beast` number, since 6 + 6 + 561 + 7 + 86 = 666.

It can be written as a sum of positive squares in 3 ways, for example, as 57471561 + 9090225 = 7581^2 + 3015^2 .

It is not an unprimeable number, because it can be changed into a prime (66561787) 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 17 ways as a sum of consecutive naturals, for example, 12940 + ... + 17336.

Almost surely, 2^66561786 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 66561786, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (74697831).

66561786 is an abundant number, since it is smaller than the sum of its proper divisors (82833876).

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

66561786 is a wasteful number, since it uses less digits than its factorization.

66561786 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4463 (or 4431 counting only the distinct ones).

The product of its digits is 362880, while the sum is 45.

The square root of 66561786 is about 8158.5406783321. The cubic root of 66561786 is about 405.2673863007.

The spelling of 66561786 in words is "sixty-six million, five hundred sixty-one thousand, seven hundred eighty-six".