66405821 has 2 divisors, whose sum is σ = 66405822. Its totient is φ = 66405820.

The previous prime is 66405799. The next prime is 66405839. The reversal of 66405821 is 12850466.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 60621796 + 5784025 = 7786^2 + 2405^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66405821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66405841) 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, 33202910 + 33202911.

It is an arithmetic number, because the mean of its divisors is an integer number (33202911).

Almost surely, 2^66405821 is an apocalyptic number.

It is an amenable number.

66405821 is a deficient number, since it is larger than the sum of its proper divisors (1).

66405821 is an equidigital number, since it uses as much as digits as its factorization.

66405821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 11520, while the sum is 32.

The square root of 66405821 is about 8148.9766842224. The cubic root of 66405821 is about 404.9506031305.

The spelling of 66405821 in words is "sixty-six million, four hundred five thousand, eight hundred twenty-one".