81406640 has 120 divisors (see below), whose sum is σ = 231971760. Its totient is φ = 26417664.

The previous prime is 81406627. The next prime is 81406643. The reversal of 81406640 is 4660418.

It is not an unprimeable number, because it can be changed into a prime (81406643) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 73934 + ... + 75026.

It is an arithmetic number, because the mean of its divisors is an integer number (1933098).

Almost surely, 2^81406640 is an apocalyptic number.

81406640 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81406640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (115985880).

81406640 is an abundant number, since it is smaller than the sum of its proper divisors (150565120).

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

81406640 is a wasteful number, since it uses less digits than its factorization.

81406640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1139 (or 1126 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 29.

The square root of 81406640 is about 9022.5628288198. The cubic root of 81406640 is about 433.3977077276.

The spelling of 81406640 in words is "eighty-one million, four hundred six thousand, six hundred forty".