81643653 has 96 divisors (see below), whose sum is σ = 156280320. Its totient is φ = 41731200.

The previous prime is 81643651. The next prime is 81643657. The reversal of 81643653 is 35634618.

81643653 is a `hidden beast` number, since 8 + 1 + 643 + 6 + 5 + 3 = 666.

It is not a de Polignac number, because 81643653 - 2¹ = 81643651 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81643651) by changing a digit.

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 95 ways as a sum of consecutive naturals, for example, 808303 + ... + 808403.

It is an arithmetic number, because the mean of its divisors is an integer number (1627920).

Almost surely, 2^81643653 is an apocalyptic number.

It is an amenable number.

81643653 is a deficient number, since it is larger than the sum of its proper divisors (74636667).

81643653 is a wasteful number, since it uses less digits than its factorization.

81643653 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 184 (or 171 counting only the distinct ones).

The product of its digits is 51840, while the sum is 36.

The square root of 81643653 is about 9035.6877436087. The cubic root of 81643653 is about 433.8179083493.

The spelling of 81643653 in words is "eighty-one million, six hundred forty-three thousand, six hundred fifty-three".