66518521 has 4 divisors (see below), whose sum is σ = 66566500. Its totient is φ = 66470544.

The previous prime is 66518513. The next prime is 66518527. The reversal of 66518521 is 12581566.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12581566 = 2 ⋅6290783.

It can be written as a sum of positive squares in 2 ways, for example, as 36433296 + 30085225 = 6036^2 + 5485^2 .

It is a cyclic number.

It is not a de Polignac number, because 66518521 - 2³ = 66518513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66518527) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21846 + ... + 24703.

It is an arithmetic number, because the mean of its divisors is an integer number (16641625).

Almost surely, 2^66518521 is an apocalyptic number.

It is an amenable number.

66518521 is a deficient number, since it is larger than the sum of its proper divisors (47979).

66518521 is a wasteful number, since it uses less digits than its factorization.

66518521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 47978.

The product of its digits is 14400, while the sum is 34.

The square root of 66518521 is about 8155.8887314627. Note that the first 3 decimals coincide. The cubic root of 66518521 is about 405.1795596618.

The spelling of 66518521 in words is "sixty-six million, five hundred eighteen thousand, five hundred twenty-one".