81785917 has 2 divisors, whose sum is σ = 81785918. Its totient is φ = 81785916.

The previous prime is 81785863. The next prime is 81785971. The reversal of 81785917 is 71958718.

Together with next prime (81785971) it forms an Ormiston pair, because they use the same digits, order apart.

It is a balanced prime because it is at equal distance from previous prime (81785863) and next prime (81785971).

It can be written as a sum of positive squares in only one way, i.e., 81342361 + 443556 = 9019^2 + 666^2 .

It is a cyclic number.

It is not a de Polignac number, because 81785917 - 2¹¹ = 81783869 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81783917) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40892958 + 40892959.

It is an arithmetic number, because the mean of its divisors is an integer number (40892959).

Almost surely, 2^81785917 is an apocalyptic number.

It is an amenable number.

81785917 is a deficient number, since it is larger than the sum of its proper divisors (1).

81785917 is an equidigital number, since it uses as much as digits as its factorization.

81785917 is an evil number, because the sum of its binary digits is even.

The product of its digits is 141120, while the sum is 46.

The square root of 81785917 is about 9043.5566565373. The cubic root of 81785917 is about 434.0697379210.

The spelling of 81785917 in words is "eighty-one million, seven hundred eighty-five thousand, nine hundred seventeen".