81081640 has 32 divisors (see below), whose sum is σ = 183503880. Its totient is φ = 32242432.

The previous prime is 81081631. The next prime is 81081643. The reversal of 81081640 is 4618018.

It can be written as a sum of positive squares in 4 ways, for example, as 56460196 + 24621444 = 7514^2 + 4962^2 .

It is a junction number, because it is equal to n+sod(n) for n = 81081599 and 81081608.

It is not an unprimeable number, because it can be changed into a prime (81081643) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1062 + ... + 12778.

Almost surely, 2^81081640 is an apocalyptic number.

It is an amenable number.

81081640 is an abundant number, since it is smaller than the sum of its proper divisors (102422240).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81081640 is a wasteful number, since it uses less digits than its factorization.

81081640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11901 (or 11897 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 28.

The square root of 81081640 is about 9004.5344132831. The cubic root of 81081640 is about 432.8201867941.

Adding to 81081640 its reverse (4618018), we get a palindrome (85699658).

The spelling of 81081640 in words is "eighty-one million, eighty-one thousand, six hundred forty".