81334782721 has 2 divisors, whose sum is σ = 81334782722. Its totient is φ = 81334782720.

The previous prime is 81334782713. The next prime is 81334782733. The reversal of 81334782721 is 12728743318.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 75193866225 + 6140916496 = 274215^2 + 78364^2 .

It is a cyclic number.

It is not a de Polignac number, because 81334782721 - 2³ = 81334782713 is a prime.

It is not a weakly prime, because it can be changed into another prime (81334782121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40667391360 + 40667391361.

It is an arithmetic number, because the mean of its divisors is an integer number (40667391361).

Almost surely, 2^81334782721 is an apocalyptic number.

It is an amenable number.

81334782721 is a deficient number, since it is larger than the sum of its proper divisors (1).

81334782721 is an equidigital number, since it uses as much as digits as its factorization.

81334782721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 451584, while the sum is 46.

The spelling of 81334782721 in words is "eighty-one billion, three hundred thirty-four million, seven hundred eighty-two thousand, seven hundred twenty-one".