81508709 has 2 divisors, whose sum is σ = 81508710. Its totient is φ = 81508708.

The previous prime is 81508699. The next prime is 81508723. The reversal of 81508709 is 90780518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 81396484 + 112225 = 9022^2 + 335^2 .

It is a cyclic number.

It is not a de Polignac number, because 81508709 - 2²⁴ = 64731493 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81508729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40754354 + 40754355.

It is an arithmetic number, because the mean of its divisors is an integer number (40754355).

Almost surely, 2^81508709 is an apocalyptic number.

It is an amenable number.

81508709 is a deficient number, since it is larger than the sum of its proper divisors (1).

81508709 is an equidigital number, since it uses as much as digits as its factorization.

81508709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 20160, while the sum is 38.

The square root of 81508709 is about 9028.2173766475. The cubic root of 81508709 is about 433.5787658303.

The spelling of 81508709 in words is "eighty-one million, five hundred eight thousand, seven hundred nine".