81820917 has 6 divisors (see below), whose sum is σ = 118185782. Its totient is φ = 54547272.

The previous prime is 81820909. The next prime is 81820931. The reversal of 81820917 is 71902818.

It can be written as a sum of positive squares in only one way, i.e., 62583921 + 19236996 = 7911^2 + 4386^2 .

It is not a de Polignac number, because 81820917 - 2³ = 81820909 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81820957) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4545598 + ... + 4545615.

Almost surely, 2^81820917 is an apocalyptic number.

It is an amenable number.

81820917 is a deficient number, since it is larger than the sum of its proper divisors (36364865).

81820917 is a wasteful number, since it uses less digits than its factorization.

81820917 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9091219 (or 9091216 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 81820917 is about 9045.4915289331. The cubic root of 81820917 is about 434.1316486375.

The spelling of 81820917 in words is "eighty-one million, eight hundred twenty thousand, nine hundred seventeen".