66906821 has 2 divisors, whose sum is σ = 66906822. Its totient is φ = 66906820.

The previous prime is 66906797. The next prime is 66906859. The reversal of 66906821 is 12860966.

It is an a-pointer prime, because the next prime (66906859) can be obtained adding 66906821 to its sum of digits (38).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 46104100 + 20802721 = 6790^2 + 4561^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66906821 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66906871) 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, 33453410 + 33453411.

It is an arithmetic number, because the mean of its divisors is an integer number (33453411).

Almost surely, 2^66906821 is an apocalyptic number.

It is an amenable number.

66906821 is a deficient number, since it is larger than the sum of its proper divisors (1).

66906821 is an equidigital number, since it uses as much as digits as its factorization.

66906821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 31104, while the sum is 38.

The square root of 66906821 is about 8179.6589782215. The cubic root of 66906821 is about 405.9664386180.

The spelling of 66906821 in words is "sixty-six million, nine hundred six thousand, eight hundred twenty-one".