81785721 has 8 divisors (see below), whose sum is σ = 109404064. Its totient is φ = 54345600.

The previous prime is 81785701. The next prime is 81785773. The reversal of 81785721 is 12758718.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81785721 - 2¹⁰ = 81784697 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81785721.

It is not an unprimeable number, because it can be changed into a prime (81785701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 43480 + ... + 45321.

It is an arithmetic number, because the mean of its divisors is an integer number (13675508).

Almost surely, 2^81785721 is an apocalyptic number.

It is an amenable number.

81785721 is a deficient number, since it is larger than the sum of its proper divisors (27618343).

81785721 is a wasteful number, since it uses less digits than its factorization.

81785721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 89111.

The product of its digits is 31360, while the sum is 39.

The square root of 81785721 is about 9043.5458200863. The cubic root of 81785721 is about 434.0693911713.

It can be divided in two parts, 81785 and 721, that multiplied together give a palindrome (58966985).

The spelling of 81785721 in words is "eighty-one million, seven hundred eighty-five thousand, seven hundred twenty-one".