81673665781949 has 2 divisors, whose sum is σ = 81673665781950. Its totient is φ = 81673665781948.

The previous prime is 81673665781909. The next prime is 81673665782143. The reversal of 81673665781949 is 94918756637618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 66337685592025 + 15335980189924 = 8144795^2 + 3916118^2 .

It is a cyclic number.

It is not a de Polignac number, because 81673665781949 - 2¹² = 81673665777853 is a prime.

It is a super-2 number, since 2×81673665781949² (a number of 29 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81673665781909) 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, 40836832890974 + 40836832890975.

It is an arithmetic number, because the mean of its divisors is an integer number (40836832890975).

Almost surely, 2^{81673665781949} is an apocalyptic number.

It is an amenable number.

81673665781949 is a deficient number, since it is larger than the sum of its proper divisors (1).

81673665781949 is an equidigital number, since it uses as much as digits as its factorization.

81673665781949 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3292047360, while the sum is 80.

The spelling of 81673665781949 in words is "eighty-one trillion, six hundred seventy-three billion, six hundred sixty-five million, seven hundred eighty-one thousand, nine hundred forty-nine".