81688909 has 2 divisors, whose sum is σ = 81688910. Its totient is φ = 81688908.

The previous prime is 81688891. The next prime is 81689033. The reversal of 81688909 is 90988618.

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., 77827684 + 3861225 = 8822^2 + 1965^2 .

It is a cyclic number.

It is not a de Polignac number, because 81688909 - 2⁵ = 81688877 is a prime.

It is a super-2 number, since 2×81688909² = 13346155707220562, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81688109) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40844454 + 40844455.

It is an arithmetic number, because the mean of its divisors is an integer number (40844455).

Almost surely, 2^81688909 is an apocalyptic number.

It is an amenable number.

81688909 is a deficient number, since it is larger than the sum of its proper divisors (1).

81688909 is an equidigital number, since it uses as much as digits as its factorization.

81688909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 248832, while the sum is 49.

The square root of 81688909 is about 9038.1916886067. The cubic root of 81688909 is about 433.8980502672.

The spelling of 81688909 in words is "eighty-one million, six hundred eighty-eight thousand, nine hundred nine".