6691477781 has 2 divisors, whose sum is σ = 6691477782. Its totient is φ = 6691477780.

The previous prime is 6691477759. The next prime is 6691477789. The reversal of 6691477781 is 1877741966.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 6650402500 + 41075281 = 81550^2 + 6409^2 .

It is a cyclic number.

It is not a de Polignac number, because 6691477781 - 2²⁶ = 6624368917 is a prime.

It is a super-2 number, since 2×6691477781² = 89551749787233367922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6691477789) 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, 3345738890 + 3345738891.

It is an arithmetic number, because the mean of its divisors is an integer number (3345738891).

Almost surely, 2^6691477781 is an apocalyptic number.

It is an amenable number.

6691477781 is a deficient number, since it is larger than the sum of its proper divisors (1).

6691477781 is an equidigital number, since it uses as much as digits as its factorization.

6691477781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3556224, while the sum is 56.

The square root of 6691477781 is about 81801.4534161833. The cubic root of 6691477781 is about 1884.4039825180.

The spelling of 6691477781 in words is "six billion, six hundred ninety-one million, four hundred seventy-seven thousand, seven hundred eighty-one".