81239681 has 2 divisors, whose sum is σ = 81239682. Its totient is φ = 81239680.

The previous prime is 81239671. The next prime is 81239693. The reversal of 81239681 is 18693218.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 78145600 + 3094081 = 8840^2 + 1759^2 .

It is a cyclic number.

It is not a de Polignac number, because 81239681 - 2²⁶ = 14130817 is a prime.

It is a super-2 number, since 2×81239681² = 13199771537963522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81239671) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40619840 + 40619841.

It is an arithmetic number, because the mean of its divisors is an integer number (40619841).

Almost surely, 2^81239681 is an apocalyptic number.

It is an amenable number.

81239681 is a deficient number, since it is larger than the sum of its proper divisors (1).

81239681 is an equidigital number, since it uses as much as digits as its factorization.

81239681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 38.

The square root of 81239681 is about 9013.3057753523. The cubic root of 81239681 is about 433.1012160555.

The spelling of 81239681 in words is "eighty-one million, two hundred thirty-nine thousand, six hundred eighty-one".