81609864 has 128 divisors (see below), whose sum is σ = 252441600. Its totient is φ = 21461760.

The previous prime is 81609851. The next prime is 81609917. The reversal of 81609864 is 46890618.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 117759 + ... + 118449.

It is an arithmetic number, because the mean of its divisors is an integer number (1972200).

Almost surely, 2^81609864 is an apocalyptic number.

81609864 is a gapful number since it is divisible by the number (84) 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 81609864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (126220800).

81609864 is an abundant number, since it is smaller than the sum of its proper divisors (170831736).

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

81609864 is a wasteful number, since it uses less digits than its factorization.

81609864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 763 (or 759 counting only the distinct ones).

The product of its (nonzero) digits is 82944, while the sum is 42.

The square root of 81609864 is about 9033.8177975870. The cubic root of 81609864 is about 433.7580535397.

The spelling of 81609864 in words is "eighty-one million, six hundred nine thousand, eight hundred sixty-four".