81639109 has 2 divisors, whose sum is σ = 81639110. Its totient is φ = 81639108.

The previous prime is 81639073. The next prime is 81639157. The reversal of 81639109 is 90193618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 72165025 + 9474084 = 8495^2 + 3078^2 .

It is a cyclic number.

It is not a de Polignac number, because 81639109 - 2⁹ = 81638597 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81639179) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40819554 + 40819555.

It is an arithmetic number, because the mean of its divisors is an integer number (40819555).

Almost surely, 2^81639109 is an apocalyptic number.

It is an amenable number.

81639109 is a deficient number, since it is larger than the sum of its proper divisors (1).

81639109 is an equidigital number, since it uses as much as digits as its factorization.

81639109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11664, while the sum is 37.

The square root of 81639109 is about 9035.4362927310. The cubic root of 81639109 is about 433.8098599378.

The spelling of 81639109 in words is "eighty-one million, six hundred thirty-nine thousand, one hundred nine".