81644138 has 4 divisors (see below), whose sum is σ = 122466210. Its totient is φ = 40822068.

The previous prime is 81644137. The next prime is 81644153. The reversal of 81644138 is 83144618.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 83144618 = 2 ⋅41572309.

It can be written as a sum of positive squares in only one way, i.e., 80766169 + 877969 = 8987^2 + 937^2 .

It is a junction number, because it is equal to n+sod(n) for n = 81644098 and 81644107.

It is not an unprimeable number, because it can be changed into a prime (81644137) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20411033 + ... + 20411036.

Almost surely, 2^81644138 is an apocalyptic number.

81644138 is a deficient number, since it is larger than the sum of its proper divisors (40822072).

81644138 is a wasteful number, since it uses less digits than its factorization.

81644138 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40822071.

The product of its digits is 18432, while the sum is 35.

The square root of 81644138 is about 9035.7145815923. The cubic root of 81644138 is about 433.8187673721.

The spelling of 81644138 in words is "eighty-one million, six hundred forty-four thousand, one hundred thirty-eight".