81909881 has 2 divisors, whose sum is σ = 81909882. Its totient is φ = 81909880.

The previous prime is 81909871. The next prime is 81909887. The reversal of 81909881 is 18890918.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 63282025 + 18627856 = 7955^2 + 4316^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81909881 is a prime.

It is a super-2 number, since 2×81909881² = 13418457210868322, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (81909887) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40954940 + 40954941.

It is an arithmetic number, because the mean of its divisors is an integer number (40954941).

Almost surely, 2^81909881 is an apocalyptic number.

It is an amenable number.

81909881 is a deficient number, since it is larger than the sum of its proper divisors (1).

81909881 is an equidigital number, since it uses as much as digits as its factorization.

81909881 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 41472, while the sum is 44.

The square root of 81909881 is about 9050.4077808682. The cubic root of 81909881 is about 434.2889356325.

The spelling of 81909881 in words is "eighty-one million, nine hundred nine thousand, eight hundred eighty-one".