81338384581 has 2 divisors, whose sum is σ = 81338384582. Its totient is φ = 81338384580.

The previous prime is 81338384563. The next prime is 81338384593. The reversal of 81338384581 is 18548383318.

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., 51151059556 + 30187325025 = 226166^2 + 173745^2 .

It is a cyclic number.

It is not a de Polignac number, because 81338384581 - 2⁷ = 81338384453 is a prime.

It is a super-2 number, since 2×81338384581² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81308384581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40669192290 + 40669192291.

It is an arithmetic number, because the mean of its divisors is an integer number (40669192291).

Almost surely, 2^81338384581 is an apocalyptic number.

It is an amenable number.

81338384581 is a deficient number, since it is larger than the sum of its proper divisors (1).

81338384581 is an equidigital number, since it uses as much as digits as its factorization.

81338384581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2211840, while the sum is 52.

The spelling of 81338384581 in words is "eighty-one billion, three hundred thirty-eight million, three hundred eighty-four thousand, five hundred eighty-one".