81728281 has 2 divisors, whose sum is σ = 81728282. Its totient is φ = 81728280.

The previous prime is 81728249. The next prime is 81728287. The reversal of 81728281 is 18282718.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 78057225 + 3671056 = 8835^2 + 1916^2 .

It is a cyclic number.

It is not a de Polignac number, because 81728281 - 2⁵ = 81728249 is a prime.

It is a super-2 number, since 2×81728281² = 13359023830429922, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81728281.

It is not a weakly prime, because it can be changed into another prime (81728287) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40864140 + 40864141.

It is an arithmetic number, because the mean of its divisors is an integer number (40864141).

Almost surely, 2^81728281 is an apocalyptic number.

It is an amenable number.

81728281 is a deficient number, since it is larger than the sum of its proper divisors (1).

81728281 is an equidigital number, since it uses as much as digits as its factorization.

81728281 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14336, while the sum is 37.

The square root of 81728281 is about 9040.3695167841. The cubic root of 81728281 is about 433.9677483873.

The spelling of 81728281 in words is "eighty-one million, seven hundred twenty-eight thousand, two hundred eighty-one".