81756417209 has 2 divisors, whose sum is σ = 81756417210. Its totient is φ = 81756417208.

The previous prime is 81756417191. The next prime is 81756417257. The reversal of 81756417209 is 90271465718.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 44437904809 + 37318512400 = 210803^2 + 193180^2 .

It is a cyclic number.

It is not a de Polignac number, because 81756417209 - 2²⁸ = 81487981753 is a prime.

It is a super-2 number, since 2×81756417209² (a number of 23 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81756417409) 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, 40878208604 + 40878208605.

It is an arithmetic number, because the mean of its divisors is an integer number (40878208605).

Almost surely, 2^81756417209 is an apocalyptic number.

It is an amenable number.

81756417209 is a deficient number, since it is larger than the sum of its proper divisors (1).

81756417209 is an equidigital number, since it uses as much as digits as its factorization.

81756417209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 846720, while the sum is 50.

The spelling of 81756417209 in words is "eighty-one billion, seven hundred fifty-six million, four hundred seventeen thousand, two hundred nine".