81635720 has 32 divisors (see below), whose sum is σ = 185316120. Its totient is φ = 32363520.

The previous prime is 81635711. The next prime is 81635753. The reversal of 81635720 is 2753618.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 53904964 + 27730756 = 7342^2 + 5266^2 .

It is a Smith number, since the sum of its digits (32) coincides with the sum of the digits of its prime factors.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4511 + ... + 13550.

Almost surely, 2^81635720 is an apocalyptic number.

It is an amenable number.

81635720 is an abundant number, since it is smaller than the sum of its proper divisors (103680400).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81635720 is a wasteful number, since it uses less digits than its factorization.

81635720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18185 (or 18181 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 32.

The square root of 81635720 is about 9035.2487514180. The cubic root of 81635720 is about 433.8038570879.

The spelling of 81635720 in words is "eighty-one million, six hundred thirty-five thousand, seven hundred twenty".