66805021 has 2 divisors, whose sum is σ = 66805022. Its totient is φ = 66805020.

The previous prime is 66804961. The next prime is 66805073. The reversal of 66805021 is 12050866.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 56475225 + 10329796 = 7515^2 + 3214^2 .

It is a cyclic number.

It is not a de Polignac number, because 66805021 - 2¹⁵ = 66772253 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66805421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33402510 + 33402511.

It is an arithmetic number, because the mean of its divisors is an integer number (33402511).

Almost surely, 2^66805021 is an apocalyptic number.

It is an amenable number.

66805021 is a deficient number, since it is larger than the sum of its proper divisors (1).

66805021 is an equidigital number, since it uses as much as digits as its factorization.

66805021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2880, while the sum is 28.

The square root of 66805021 is about 8173.4338560974. The cubic root of 66805021 is about 405.7604388873.

Adding to 66805021 its reverse (12050866), we get a palindrome (78855887).

The spelling of 66805021 in words is "sixty-six million, eight hundred five thousand, twenty-one".