81691344313 has 2 divisors, whose sum is σ = 81691344314. Its totient is φ = 81691344312.

The previous prime is 81691344299. The next prime is 81691344353. The reversal of 81691344313 is 31344319618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 80331431184 + 1359913129 = 283428^2 + 36877^2 .

It is a cyclic number.

It is not a de Polignac number, because 81691344313 - 2⁹ = 81691343801 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81691344313.

It is not a weakly prime, because it can be changed into another prime (81691344353) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40845672156 + 40845672157.

It is an arithmetic number, because the mean of its divisors is an integer number (40845672157).

Almost surely, 2^81691344313 is an apocalyptic number.

It is an amenable number.

81691344313 is a deficient number, since it is larger than the sum of its proper divisors (1).

81691344313 is an equidigital number, since it uses as much as digits as its factorization.

81691344313 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 186624, while the sum is 43.

The spelling of 81691344313 in words is "eighty-one billion, six hundred ninety-one million, three hundred forty-four thousand, three hundred thirteen".