66213509 has 2 divisors, whose sum is σ = 66213510. Its totient is φ = 66213508.

The previous prime is 66213503. The next prime is 66213523. The reversal of 66213509 is 90531266.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50452609 + 15760900 = 7103^2 + 3970^2 .

It is a cyclic number.

It is not a de Polignac number, because 66213509 - 2⁸ = 66213253 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66213503) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33106754 + 33106755.

It is an arithmetic number, because the mean of its divisors is an integer number (33106755).

Almost surely, 2^66213509 is an apocalyptic number.

It is an amenable number.

66213509 is a deficient number, since it is larger than the sum of its proper divisors (1).

66213509 is an equidigital number, since it uses as much as digits as its factorization.

66213509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 9720, while the sum is 32.

The square root of 66213509 is about 8137.1683649781. The cubic root of 66213509 is about 404.5593113340.

The spelling of 66213509 in words is "sixty-six million, two hundred thirteen thousand, five hundred nine".