66555781 has 2 divisors, whose sum is σ = 66555782. Its totient is φ = 66555780.

The previous prime is 66555773. The next prime is 66555793. The reversal of 66555781 is 18755566.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 37933281 + 28622500 = 6159^2 + 5350^2 .

It is a cyclic number.

It is not a de Polignac number, because 66555781 - 2³ = 66555773 is a prime.

It is a super-3 number, since 3×66555781³ (a number of 24 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66555581) 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, 33277890 + 33277891.

It is an arithmetic number, because the mean of its divisors is an integer number (33277891).

Almost surely, 2^66555781 is an apocalyptic number.

It is an amenable number.

66555781 is a deficient number, since it is larger than the sum of its proper divisors (1).

66555781 is an equidigital number, since it uses as much as digits as its factorization.

66555781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 252000, while the sum is 43.

The square root of 66555781 is about 8158.1726507840. The cubic root of 66555781 is about 405.2551986077.

The spelling of 66555781 in words is "sixty-six million, five hundred fifty-five thousand, seven hundred eighty-one".