81917909 has 2 divisors, whose sum is σ = 81917910. Its totient is φ = 81917908.

The previous prime is 81917863. The next prime is 81917977. The reversal of 81917909 is 90971918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 60109009 + 21808900 = 7753^2 + 4670^2 .

It is a cyclic number.

It is not a de Polignac number, because 81917909 - 2²⁰ = 80869333 is a prime.

It is equal to p_4774877 and since 81917909 and 4774877 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81917909.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81917989) 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, 40958954 + 40958955.

It is an arithmetic number, because the mean of its divisors is an integer number (40958955).

Almost surely, 2^81917909 is an apocalyptic number.

It is an amenable number.

81917909 is a deficient number, since it is larger than the sum of its proper divisors (1).

81917909 is an equidigital number, since it uses as much as digits as its factorization.

81917909 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 40824, while the sum is 44.

The square root of 81917909 is about 9050.8512859289. The cubic root of 81917909 is about 434.3031234107.

The spelling of 81917909 in words is "eighty-one million, nine hundred seventeen thousand, nine hundred nine".