81409840 has 20 divisors (see below), whose sum is σ = 189278064. Its totient is φ = 32563904.

The previous prime is 81409837. The next prime is 81409841. The reversal of 81409840 is 4890418.

It is a tau number, because it is divible by the number of its divisors (20).

It is a junction number, because it is equal to n+sod(n) for n = 81409796 and 81409805.

It is not an unprimeable number, because it can be changed into a prime (81409841) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 508732 + ... + 508891.

Almost surely, 2^81409840 is an apocalyptic number.

81409840 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81409840 is an abundant number, since it is smaller than the sum of its proper divisors (107868224).

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

81409840 is a wasteful number, since it uses less digits than its factorization.

81409840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1017636 (or 1017630 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 34.

The square root of 81409840 is about 9022.7401602839. The cubic root of 81409840 is about 433.4033864392.

The spelling of 81409840 in words is "eighty-one million, four hundred nine thousand, eight hundred forty".