81800067721 has 2 divisors, whose sum is σ = 81800067722. Its totient is φ = 81800067720.

The previous prime is 81800067719. The next prime is 81800067743. The reversal of 81800067721 is 12776000818.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 79648128400 + 2151939321 = 282220^2 + 46389^2 .

It is a cyclic number.

It is not a de Polignac number, because 81800067721 - 2¹ = 81800067719 is a prime.

It is a super-2 number, since 2×81800067721² (a number of 23 digits) contains 22 as substring.

Together with 81800067719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81800067121) 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, 40900033860 + 40900033861.

It is an arithmetic number, because the mean of its divisors is an integer number (40900033861).

Almost surely, 2^81800067721 is an apocalyptic number.

It is an amenable number.

81800067721 is a deficient number, since it is larger than the sum of its proper divisors (1).

81800067721 is an equidigital number, since it uses as much as digits as its factorization.

81800067721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 37632, while the sum is 40.

The spelling of 81800067721 in words is "eighty-one billion, eight hundred million, sixty-seven thousand, seven hundred twenty-one".