81605880 has 160 divisors (see below), whose sum is σ = 278348400. Its totient is φ = 21441024.

The previous prime is 81605869. The next prime is 81605891. The reversal of 81605880 is 8850618.

It is an interprime number because it is at equal distance from previous prime (81605869) and next prime (81605891).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 288219 + ... + 288501.

Almost surely, 2^81605880 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81605880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (139174200).

81605880 is an abundant number, since it is smaller than the sum of its proper divisors (196742520).

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

81605880 is a wasteful number, since it uses less digits than its factorization.

81605880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 395 (or 382 counting only the distinct ones).

The product of its (nonzero) digits is 15360, while the sum is 36.

The square root of 81605880 is about 9033.5972901165. The cubic root of 81605880 is about 433.7509950784.

The spelling of 81605880 in words is "eighty-one million, six hundred five thousand, eight hundred eighty".