81681642149 has 2 divisors, whose sum is σ = 81681642150. Its totient is φ = 81681642148.

The previous prime is 81681642103. The next prime is 81681642197. The reversal of 81681642149 is 94124618618.

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., 62997486049 + 18684156100 = 250993^2 + 136690^2 .

It is a cyclic number.

It is not a de Polignac number, because 81681642149 - 2⁸ = 81681641893 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 81681642097 and 81681642106.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81681642349) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40840821074 + 40840821075.

It is an arithmetic number, because the mean of its divisors is an integer number (40840821075).

Almost surely, 2^81681642149 is an apocalyptic number.

It is an amenable number.

81681642149 is a deficient number, since it is larger than the sum of its proper divisors (1).

81681642149 is an equidigital number, since it uses as much as digits as its factorization.

81681642149 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 663552, while the sum is 50.

The spelling of 81681642149 in words is "eighty-one billion, six hundred eighty-one million, six hundred forty-two thousand, one hundred forty-nine".