81729618181 has 2 divisors, whose sum is σ = 81729618182. Its totient is φ = 81729618180.

The previous prime is 81729618167. The next prime is 81729618211. The reversal of 81729618181 is 18181692718.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 70442468100 + 11287150081 = 265410^2 + 106241^2 .

It is a cyclic number.

It is not a de Polignac number, because 81729618181 - 2²⁵ = 81696063749 is a prime.

It is a super-2 number, since 2×81729618181² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81729618101) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40864809090 + 40864809091.

It is an arithmetic number, because the mean of its divisors is an integer number (40864809091).

Almost surely, 2^81729618181 is an apocalyptic number.

It is an amenable number.

81729618181 is a deficient number, since it is larger than the sum of its proper divisors (1).

81729618181 is an equidigital number, since it uses as much as digits as its factorization.

81729618181 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 387072, while the sum is 52.

The spelling of 81729618181 in words is "eighty-one billion, seven hundred twenty-nine million, six hundred eighteen thousand, one hundred eighty-one".