81640040 has 16 divisors (see below), whose sum is σ = 183690180. Its totient is φ = 32656000.

The previous prime is 81640007. The next prime is 81640049. The reversal of 81640040 is 4004618.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 76983076 + 4656964 = 8774^2 + 2158^2 .

It is a super-2 number, since 2×81640040² = 13330192262403200, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81639988 and 81640015.

It is not an unprimeable number, because it can be changed into a prime (81640049) 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, 1020461 + ... + 1020540.

Almost surely, 2^81640040 is an apocalyptic number.

It is an amenable number.

81640040 is an abundant number, since it is smaller than the sum of its proper divisors (102050140).

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

81640040 is a wasteful number, since it uses less digits than its factorization.

81640040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2041012 (or 2041008 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 23.

The square root of 81640040 is about 9035.4878119557. The cubic root of 81640040 is about 433.8115089655.

Adding to 81640040 its reverse (4004618), we get a palindrome (85644658).

The spelling of 81640040 in words is "eighty-one million, six hundred forty thousand, forty".