81705121 has 2 divisors, whose sum is σ = 81705122. Its totient is φ = 81705120.

The previous prime is 81705109. The next prime is 81705133. The reversal of 81705121 is 12150718.

It is a balanced prime because it is at equal distance from previous prime (81705109) and next prime (81705133).

It can be written as a sum of positive squares in only one way, i.e., 81703521 + 1600 = 9039^2 + 40^2 .

It is a cyclic number.

It is not a de Polignac number, because 81705121 - 2⁵ = 81705089 is a prime.

It is not a weakly prime, because it can be changed into another prime (81705161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40852560 + 40852561.

It is an arithmetic number, because the mean of its divisors is an integer number (40852561).

Almost surely, 2^81705121 is an apocalyptic number.

It is an amenable number.

81705121 is a deficient number, since it is larger than the sum of its proper divisors (1).

81705121 is an equidigital number, since it uses as much as digits as its factorization.

81705121 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 560, while the sum is 25.

The square root of 81705121 is about 9039.0885049323. The cubic root of 81705121 is about 433.9267522048.

Adding to 81705121 its reverse (12150718), we get a palindrome (93855839).

The spelling of 81705121 in words is "eighty-one million, seven hundred five thousand, one hundred twenty-one".