81817121 has 2 divisors, whose sum is σ = 81817122. Its totient is φ = 81817120.

The previous prime is 81817111. The next prime is 81817147. The reversal of 81817121 is 12171818.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 73290721 + 8526400 = 8561^2 + 2920^2 .

It is a cyclic number.

It is not a de Polignac number, because 81817121 - 2²² = 77622817 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81817111) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40908560 + 40908561.

It is an arithmetic number, because the mean of its divisors is an integer number (40908561).

Almost surely, 2^81817121 is an apocalyptic number.

It is an amenable number.

81817121 is a deficient number, since it is larger than the sum of its proper divisors (1).

81817121 is an equidigital number, since it uses as much as digits as its factorization.

81817121 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 896, while the sum is 29.

The square root of 81817121 is about 9045.2816982115. The cubic root of 81817121 is about 434.1249348317.

Adding to 81817121 its reverse (12171818), we get a palindrome (93988939).

The spelling of 81817121 in words is "eighty-one million, eight hundred seventeen thousand, one hundred twenty-one".