66555221 has 4 divisors (see below), whose sum is σ = 70470252. Its totient is φ = 62640192.

The previous prime is 66555199. The next prime is 66555241. The reversal of 66555221 is 12255566.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 47458321 + 19096900 = 6889^2 + 4370^2 .

It is a cyclic number.

It is not a de Polignac number, because 66555221 - 2¹⁰ = 66554197 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66555241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1957490 + ... + 1957523.

It is an arithmetic number, because the mean of its divisors is an integer number (17617563).

Almost surely, 2^66555221 is an apocalyptic number.

It is an amenable number.

66555221 is a deficient number, since it is larger than the sum of its proper divisors (3915031).

66555221 is a wasteful number, since it uses less digits than its factorization.

66555221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3915030.

The product of its digits is 18000, while the sum is 32.

The square root of 66555221 is about 8158.1383293004. The cubic root of 66555221 is about 405.2540619995.

The spelling of 66555221 in words is "sixty-six million, five hundred fifty-five thousand, two hundred twenty-one".