81639841 has 2 divisors, whose sum is σ = 81639842. Its totient is φ = 81639840.

The previous prime is 81639839. The next prime is 81639889. The reversal of 81639841 is 14893618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 59737441 + 21902400 = 7729^2 + 4680^2 .

It is a cyclic number.

It is not a de Polignac number, because 81639841 - 2¹ = 81639839 is a prime.

Together with 81639839, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 81639794 and 81639803.

It is not a weakly prime, because it can be changed into another prime (81639821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40819920 + 40819921.

It is an arithmetic number, because the mean of its divisors is an integer number (40819921).

Almost surely, 2^81639841 is an apocalyptic number.

It is an amenable number.

81639841 is a deficient number, since it is larger than the sum of its proper divisors (1).

81639841 is an equidigital number, since it uses as much as digits as its factorization.

81639841 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 41472, while the sum is 40.

The square root of 81639841 is about 9035.4767998153. The cubic root of 81639841 is about 433.8111564891.

The spelling of 81639841 in words is "eighty-one million, six hundred thirty-nine thousand, eight hundred forty-one".