66239821 has 2 divisors, whose sum is σ = 66239822. Its totient is φ = 66239820.

The previous prime is 66239819. The next prime is 66239867. The reversal of 66239821 is 12893266.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 59505796 + 6734025 = 7714^2 + 2595^2 .

It is a cyclic number.

It is not a de Polignac number, because 66239821 - 2¹ = 66239819 is a prime.

It is a super-2 number, since 2×66239821² = 8775427772224082, which contains 22 as substring.

Together with 66239819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66239801) 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, 33119910 + 33119911.

It is an arithmetic number, because the mean of its divisors is an integer number (33119911).

Almost surely, 2^66239821 is an apocalyptic number.

It is an amenable number.

66239821 is a deficient number, since it is larger than the sum of its proper divisors (1).

66239821 is an equidigital number, since it uses as much as digits as its factorization.

66239821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 31104, while the sum is 37.

The square root of 66239821 is about 8138.7849830303. The cubic root of 66239821 is about 404.6128923180.

The spelling of 66239821 in words is "sixty-six million, two hundred thirty-nine thousand, eight hundred twenty-one".