66217020721 has 2 divisors, whose sum is σ = 66217020722. Its totient is φ = 66217020720.

The previous prime is 66217020713. The next prime is 66217020761. The reversal of 66217020721 is 12702071266.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 40597817121 + 25619203600 = 201489^2 + 160060^2 .

It is a cyclic number.

It is not a de Polignac number, because 66217020721 - 2³ = 66217020713 is a prime.

It is not a weakly prime, because it can be changed into another prime (66217020761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33108510360 + 33108510361.

It is an arithmetic number, because the mean of its divisors is an integer number (33108510361).

Almost surely, 2^66217020721 is an apocalyptic number.

It is an amenable number.

66217020721 is a deficient number, since it is larger than the sum of its proper divisors (1).

66217020721 is an equidigital number, since it uses as much as digits as its factorization.

66217020721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 14112, while the sum is 34.

Adding to 66217020721 its reverse (12702071266), we get a palindrome (78919091987).

The spelling of 66217020721 in words is "sixty-six billion, two hundred seventeen million, twenty thousand, seven hundred twenty-one".