81697409 has 2 divisors, whose sum is σ = 81697410. Its totient is φ = 81697408.

The previous prime is 81697387. The next prime is 81697411. The reversal of 81697409 is 90479618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 75082225 + 6615184 = 8665^2 + 2572^2 .

It is a cyclic number.

It is not a de Polignac number, because 81697409 - 2⁸ = 81697153 is a prime.

It is a super-3 number, since 3×81697409³ (a number of 25 digits) contains 333 as substring.

Together with 81697411, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81697409.

It is not a weakly prime, because it can be changed into another prime (81697309) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40848704 + 40848705.

It is an arithmetic number, because the mean of its divisors is an integer number (40848705).

Almost surely, 2^81697409 is an apocalyptic number.

It is an amenable number.

81697409 is a deficient number, since it is larger than the sum of its proper divisors (1).

81697409 is an equidigital number, since it uses as much as digits as its factorization.

81697409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 108864, while the sum is 44.

The square root of 81697409 is about 9038.6619031801. The cubic root of 81697409 is about 433.9130992523.

The spelling of 81697409 in words is "eighty-one million, six hundred ninety-seven thousand, four hundred nine".