81638642 has 6 divisors (see below), whose sum is σ = 122477133. Its totient is φ = 40812932.

The previous prime is 81638633. The next prime is 81638647. The reversal of 81638642 is 24683618.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 45144961 + 36493681 = 6719^2 + 6041^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=6389.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81638596 and 81638605.

It is not an unprimeable number, because it can be changed into a prime (81638647) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 9584 + ... + 15972.

Almost surely, 2^81638642 is an apocalyptic number.

81638642 is a deficient number, since it is larger than the sum of its proper divisors (40838491).

81638642 is an frugal number, since it uses more digits than its factorization.

81638642 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12780 (or 6391 counting only the distinct ones).

The product of its digits is 55296, while the sum is 38.

The square root of 81638642 is about 9035.4104500017. The cubic root of 81638642 is about 433.8090327624.

The spelling of 81638642 in words is "eighty-one million, six hundred thirty-eight thousand, six hundred forty-two".