66090821 has 2 divisors, whose sum is σ = 66090822. Its totient is φ = 66090820.

The previous prime is 66090763. The next prime is 66090839. The reversal of 66090821 is 12809066.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 65788321 + 302500 = 8111^2 + 550^2 .

It is a cyclic number.

It is not a de Polignac number, because 66090821 - 2¹⁸ = 65828677 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66090851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33045410 + 33045411.

It is an arithmetic number, because the mean of its divisors is an integer number (33045411).

Almost surely, 2^66090821 is an apocalyptic number.

It is an amenable number.

66090821 is a deficient number, since it is larger than the sum of its proper divisors (1).

66090821 is an equidigital number, since it uses as much as digits as its factorization.

66090821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5184, while the sum is 32.

The square root of 66090821 is about 8129.6261291649. The cubic root of 66090821 is about 404.3092855143.

Adding to 66090821 its reverse (12809066), we get a palindrome (78899887).

The spelling of 66090821 in words is "sixty-six million, ninety thousand, eight hundred twenty-one".