81605440 has 112 divisors (see below), whose sum is σ = 235256832. Its totient is φ = 26320896.

The previous prime is 81605431. The next prime is 81605453. The reversal of 81605440 is 4450618.

It is a tau number, because it is divible by the number of its divisors (112).

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a junction number, because it is equal to n+sod(n) for n = 81605399 and 81605408.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 37009 + ... + 39151.

Almost surely, 2^81605440 is an apocalyptic number.

81605440 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 81605440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (117628416).

81605440 is an abundant number, since it is smaller than the sum of its proper divisors (153651392).

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

81605440 is a wasteful number, since it uses less digits than its factorization.

81605440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2184 (or 2174 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 28.

The square root of 81605440 is about 9033.5729365517. The cubic root of 81605440 is about 433.7502155153.

The spelling of 81605440 in words is "eighty-one million, six hundred five thousand, four hundred forty".