81661725 has 18 divisors (see below), whose sum is σ = 146265626. Its totient is φ = 43552800.

The previous prime is 81661721. The next prime is 81661733. The reversal of 81661725 is 52716618.

81661725 is a `hidden beast` number, since 8 + 16 + 617 + 25 = 666.

It can be written as a sum of positive squares in 3 ways, for example, as 715716 + 80946009 = 846^2 + 8997^2 .

It is not a de Polignac number, because 81661725 - 2² = 81661721 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 81661725.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81661721) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 181246 + ... + 181695.

Almost surely, 2^81661725 is an apocalyptic number.

It is an amenable number.

81661725 is a deficient number, since it is larger than the sum of its proper divisors (64603901).

81661725 is a wasteful number, since it uses less digits than its factorization.

81661725 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 362957 (or 362949 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 81661725 is about 9036.6877228330. The cubic root of 81661725 is about 433.8499148334.

The spelling of 81661725 in words is "eighty-one million, six hundred sixty-one thousand, seven hundred twenty-five".