66009521 has 4 divisors (see below), whose sum is σ = 69892452. Its totient is φ = 62126592.

The previous prime is 66009497. The next prime is 66009523. The reversal of 66009521 is 12590066.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12590066 = 2 ⋅6295033.

It can be written as a sum of positive squares in 2 ways, for example, as 56175025 + 9834496 = 7495^2 + 3136^2 .

It is a cyclic number.

It is not a de Polignac number, because 66009521 - 2¹⁰ = 66008497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66009523) 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, 1941440 + ... + 1941473.

It is an arithmetic number, because the mean of its divisors is an integer number (17473113).

Almost surely, 2^66009521 is an apocalyptic number.

It is an amenable number.

66009521 is a deficient number, since it is larger than the sum of its proper divisors (3882931).

66009521 is a wasteful number, since it uses less digits than its factorization.

66009521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3882930.

The product of its (nonzero) digits is 3240, while the sum is 29.

The square root of 66009521 is about 8124.6243605474. The cubic root of 66009521 is about 404.1434337775.

Adding to 66009521 its reverse (12590066), we get a palindrome (78599587).

The spelling of 66009521 in words is "sixty-six million, nine thousand, five hundred twenty-one".