81638 has 4 divisors (see below), whose sum is σ = 122460. Its totient is φ = 40818.

The previous prime is 81637. The next prime is 81647. The reversal of 81638 is 83618.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 83618 = 2 ⋅41809.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 81638.

It is not an unprimeable number, because it can be changed into a prime (81637) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20408 + ... + 20411.

It is an arithmetic number, because the mean of its divisors is an integer number (30615).

2⁸¹⁶³⁸ is an apocalyptic number.

81638 is a deficient number, since it is larger than the sum of its proper divisors (40822).

81638 is a wasteful number, since it uses less digits than its factorization.

81638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40821.

The product of its digits is 1152, while the sum is 26.

The square root of 81638 is about 285.7236427039. The cubic root of 81638 is about 43.3807895612.

The spelling of 81638 in words is "eighty-one thousand, six hundred thirty-eight".