81244781 has 2 divisors, whose sum is σ = 81244782. Its totient is φ = 81244780.

The previous prime is 81244777. The next prime is 81244861. The reversal of 81244781 is 18744218.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 80389156 + 855625 = 8966^2 + 925^2 .

It is a cyclic number.

It is not a de Polignac number, because 81244781 - 2² = 81244777 is a prime.

It is a super-2 number, since 2×81244781² = 13201428879475922, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81244981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40622390 + 40622391.

It is an arithmetic number, because the mean of its divisors is an integer number (40622391).

Almost surely, 2^81244781 is an apocalyptic number.

It is an amenable number.

81244781 is a deficient number, since it is larger than the sum of its proper divisors (1).

81244781 is an equidigital number, since it uses as much as digits as its factorization.

81244781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14336, while the sum is 35.

The square root of 81244781 is about 9013.5886859785. The cubic root of 81244781 is about 433.1102788270.

Adding to 81244781 its reverse (18744218), we get a palindrome (99988999).

The spelling of 81244781 in words is "eighty-one million, two hundred forty-four thousand, seven hundred eighty-one".