81191660 has 72 divisors (see below), whose sum is σ = 197742384. Its totient is φ = 27765760.

The previous prime is 81191641. The next prime is 81191681. The reversal of 81191660 is 6619118.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 62942 + ... + 64218.

It is an arithmetic number, because the mean of its divisors is an integer number (2746422).

Almost surely, 2^81191660 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 81191660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (98871192).

81191660 is an abundant number, since it is smaller than the sum of its proper divisors (116550724).

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

81191660 is a wasteful number, since it uses less digits than its factorization.

81191660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1331 (or 1312 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 32.

The square root of 81191660 is about 9010.6414865979. The cubic root of 81191660 is about 433.0158634606.

It can be divided in two parts, 8119 and 1660, that added together give a palindrome (9779).

The spelling of 81191660 in words is "eighty-one million, one hundred ninety-one thousand, six hundred sixty".