66779981 has 2 divisors, whose sum is σ = 66779982. Its totient is φ = 66779980.

The previous prime is 66779969. The next prime is 66779987. The reversal of 66779981 is 18997766.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66275881 + 504100 = 8141^2 + 710^2 .

It is a cyclic number.

It is not a de Polignac number, because 66779981 - 2¹⁸ = 66517837 is a prime.

It is a super-2 number, since 2×66779981² = 8919131724720722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66779987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33389990 + 33389991.

It is an arithmetic number, because the mean of its divisors is an integer number (33389991).

Almost surely, 2^66779981 is an apocalyptic number.

It is an amenable number.

66779981 is a deficient number, since it is larger than the sum of its proper divisors (1).

66779981 is an equidigital number, since it uses as much as digits as its factorization.

66779981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1143072, while the sum is 53.

The square root of 66779981 is about 8171.9019206058. The cubic root of 66779981 is about 405.7097365552.

The spelling of 66779981 in words is "sixty-six million, seven hundred seventy-nine thousand, nine hundred eighty-one".