81856981 has 2 divisors, whose sum is σ = 81856982. Its totient is φ = 81856980.

The previous prime is 81856979. The next prime is 81856991. The reversal of 81856981 is 18965818.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 81270225 + 586756 = 9015^2 + 766^2 .

It is a cyclic number.

It is not a de Polignac number, because 81856981 - 2¹ = 81856979 is a prime.

It is a super-2 number, since 2×81856981² = 13401130676868722, which contains 22 as substring.

Together with 81856979, it forms a pair of twin primes.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81856991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40928490 + 40928491.

It is an arithmetic number, because the mean of its divisors is an integer number (40928491).

Almost surely, 2^81856981 is an apocalyptic number.

It is an amenable number.

81856981 is a deficient number, since it is larger than the sum of its proper divisors (1).

81856981 is an equidigital number, since it uses as much as digits as its factorization.

81856981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 138240, while the sum is 46.

The square root of 81856981 is about 9047.4847886029. The cubic root of 81856981 is about 434.1954229738.

The spelling of 81856981 in words is "eighty-one million, eight hundred fifty-six thousand, nine hundred eighty-one".