81680520409 has 2 divisors, whose sum is σ = 81680520410. Its totient is φ = 81680520408.

The previous prime is 81680520391. The next prime is 81680520431. The reversal of 81680520409 is 90402508618.

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., 66772110409 + 14908410000 = 258403^2 + 122100^2 .

It is a cyclic number.

It is not a de Polignac number, because 81680520409 - 2¹⁵ = 81680487641 is a prime.

It is a super-3 number, since 3×81680520409³ (a number of 34 digits) contains 333 as substring.

It is not a weakly prime, because it can be changed into another prime (81680520499) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40840260204 + 40840260205.

It is an arithmetic number, because the mean of its divisors is an integer number (40840260205).

Almost surely, 2^81680520409 is an apocalyptic number.

It is an amenable number.

81680520409 is a deficient number, since it is larger than the sum of its proper divisors (1).

81680520409 is an equidigital number, since it uses as much as digits as its factorization.

81680520409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 138240, while the sum is 43.

The spelling of 81680520409 in words is "eighty-one billion, six hundred eighty million, five hundred twenty thousand, four hundred nine".