66156781 has 2 divisors, whose sum is σ = 66156782. Its totient is φ = 66156780.

The previous prime is 66156751. The next prime is 66156829. The reversal of 66156781 is 18765166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 37319881 + 28836900 = 6109^2 + 5370^2 .

It is a cyclic number.

It is not a de Polignac number, because 66156781 - 2⁵ = 66156749 is a prime.

It is a super-2 number, since 2×66156781² = 8753439344563922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66156721) 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, 33078390 + 33078391.

It is an arithmetic number, because the mean of its divisors is an integer number (33078391).

Almost surely, 2^66156781 is an apocalyptic number.

It is an amenable number.

66156781 is a deficient number, since it is larger than the sum of its proper divisors (1).

66156781 is an equidigital number, since it uses as much as digits as its factorization.

66156781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 60480, while the sum is 40.

The square root of 66156781 is about 8133.6818846080. The cubic root of 66156781 is about 404.4437437904.

The spelling of 66156781 in words is "sixty-six million, one hundred fifty-six thousand, seven hundred eighty-one".