81661653 has 6 divisors (see below), whose sum is σ = 117955734. Its totient is φ = 54441096.

The previous prime is 81661637. The next prime is 81661663. The reversal of 81661653 is 35616618.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 81595089 + 66564 = 9033^2 + 258^2 .

It is not a de Polignac number, because 81661653 - 2⁴ = 81661637 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81661663) 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, 4536750 + ... + 4536767.

It is an arithmetic number, because the mean of its divisors is an integer number (19659289).

Almost surely, 2^81661653 is an apocalyptic number.

It is an amenable number.

81661653 is a deficient number, since it is larger than the sum of its proper divisors (36294081).

81661653 is a wasteful number, since it uses less digits than its factorization.

81661653 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9073523 (or 9073520 counting only the distinct ones).

The product of its digits is 25920, while the sum is 36.

The square root of 81661653 is about 9036.6837390715. The cubic root of 81661653 is about 433.8497873269.

It can be divided in two parts, 8 and 1661653, that added together give a palindrome (1661661).

The spelling of 81661653 in words is "eighty-one million, six hundred sixty-one thousand, six hundred fifty-three".