81638441 has 4 divisors (see below), whose sum is σ = 82186500. Its totient is φ = 81090384.

The previous prime is 81638419. The next prime is 81638443. The reversal of 81638441 is 14483618.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7678441 + 73960000 = 2771^2 + 8600^2 .

It is a cyclic number.

It is not a de Polignac number, because 81638441 - 2⁶ = 81638377 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81638443) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 273806 + ... + 274103.

It is an arithmetic number, because the mean of its divisors is an integer number (20546625).

Almost surely, 2^81638441 is an apocalyptic number.

It is an amenable number.

81638441 is a deficient number, since it is larger than the sum of its proper divisors (548059).

81638441 is a wasteful number, since it uses less digits than its factorization.

81638441 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 548058.

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

The square root of 81638441 is about 9035.3993270912. The cubic root of 81638441 is about 433.8086767395.

The spelling of 81638441 in words is "eighty-one million, six hundred thirty-eight thousand, four hundred forty-one".