66656209 has 2 divisors, whose sum is σ = 66656210. Its totient is φ = 66656208.

The previous prime is 66656207. The next prime is 66656243. The reversal of 66656209 is 90265666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 58476609 + 8179600 = 7647^2 + 2860^2 .

It is a cyclic number.

It is not a de Polignac number, because 66656209 - 2¹ = 66656207 is a prime.

Together with 66656207, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (66656207) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33328104 + 33328105.

It is an arithmetic number, because the mean of its divisors is an integer number (33328105).

Almost surely, 2^66656209 is an apocalyptic number.

It is an amenable number.

66656209 is a deficient number, since it is larger than the sum of its proper divisors (1).

66656209 is an equidigital number, since it uses as much as digits as its factorization.

66656209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 116640, while the sum is 40.

The square root of 66656209 is about 8164.3253854804. The cubic root of 66656209 is about 405.4589300492.

The spelling of 66656209 in words is "sixty-six million, six hundred fifty-six thousand, two hundred nine".