81691920469 has 2 divisors, whose sum is σ = 81691920470. Its totient is φ = 81691920468.

The previous prime is 81691920413. The next prime is 81691920473. The reversal of 81691920469 is 96402919618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 80786692900 + 905227569 = 284230^2 + 30087^2 .

It is a cyclic number.

It is not a de Polignac number, because 81691920469 - 2⁷ = 81691920341 is a prime.

It is a super-2 number, since 2×81691920469² (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 (81691921469) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40845960234 + 40845960235.

It is an arithmetic number, because the mean of its divisors is an integer number (40845960235).

Almost surely, 2^81691920469 is an apocalyptic number.

It is an amenable number.

81691920469 is a deficient number, since it is larger than the sum of its proper divisors (1).

81691920469 is an equidigital number, since it uses as much as digits as its factorization.

81691920469 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1679616, while the sum is 55.

The spelling of 81691920469 in words is "eighty-one billion, six hundred ninety-one million, nine hundred twenty thousand, four hundred sixty-nine".