66205621 has 2 divisors, whose sum is σ = 66205622. Its totient is φ = 66205620.

The previous prime is 66205613. The next prime is 66205631. The reversal of 66205621 is 12650266.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 63600625 + 2604996 = 7975^2 + 1614^2 .

It is a cyclic number.

It is not a de Polignac number, because 66205621 - 2³ = 66205613 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 66205621.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66205631) 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 as a sum of consecutive naturals, namely, 33102810 + 33102811.

It is an arithmetic number, because the mean of its divisors is an integer number (33102811).

Almost surely, 2^66205621 is an apocalyptic number.

It is an amenable number.

66205621 is a deficient number, since it is larger than the sum of its proper divisors (1).

66205621 is an equidigital number, since it uses as much as digits as its factorization.

66205621 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 66205621 is about 8136.6836610501. The cubic root of 66205621 is about 404.5432456770.

Adding to 66205621 its reverse (12650266), we get a palindrome (78855887).

The spelling of 66205621 in words is "sixty-six million, two hundred five thousand, six hundred twenty-one".