81811817 has 2 divisors, whose sum is σ = 81811818. Its totient is φ = 81811816.

The previous prime is 81811811. The next prime is 81811831. The reversal of 81811817 is 71811818.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 67831696 + 13980121 = 8236^2 + 3739^2 .

It is a cyclic number.

It is not a de Polignac number, because 81811817 - 2¹⁸ = 81549673 is a prime.

It is not a weakly prime, because it can be changed into another prime (81811811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40905908 + 40905909.

It is an arithmetic number, because the mean of its divisors is an integer number (40905909).

Almost surely, 2^81811817 is an apocalyptic number.

It is an amenable number.

81811817 is a deficient number, since it is larger than the sum of its proper divisors (1).

81811817 is an equidigital number, since it uses as much as digits as its factorization.

81811817 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3584, while the sum is 35.

The square root of 81811817 is about 9044.9885019275. The cubic root of 81811817 is about 434.1155535499.

Subtracting from 81811817 its reverse (71811818), we obtain a palindrome (9999999).

It can be divided in two parts, 81811 and 817, that added together give a palindrome (82628).

The spelling of 81811817 in words is "eighty-one million, eight hundred eleven thousand, eight hundred seventeen".