81318709 has 2 divisors, whose sum is σ = 81318710. Its totient is φ = 81318708.

The previous prime is 81318659. The next prime is 81318779. The reversal of 81318709 is 90781318.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 77000625 + 4318084 = 8775^2 + 2078^2 .

It is a cyclic number.

It is not a de Polignac number, because 81318709 - 2¹⁷ = 81187637 is a prime.

It is a super-2 number, since 2×81318709² = 13225464866853362, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81318779) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40659354 + 40659355.

It is an arithmetic number, because the mean of its divisors is an integer number (40659355).

Almost surely, 2^81318709 is an apocalyptic number.

It is an amenable number.

81318709 is a deficient number, since it is larger than the sum of its proper divisors (1).

81318709 is an equidigital number, since it uses as much as digits as its factorization.

81318709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12096, while the sum is 37.

The square root of 81318709 is about 9017.6886728252. The cubic root of 81318709 is about 433.2416073439.

The spelling of 81318709 in words is "eighty-one million, three hundred eighteen thousand, seven hundred nine".