81231660 has 120 divisors (see below), whose sum is σ = 261255456. Its totient is φ = 21116160.

The previous prime is 81231649. The next prime is 81231673. The reversal of 81231660 is 6613218.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 65809 + ... + 67031.

Almost surely, 2^81231660 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 81231660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (130627728).

81231660 is an abundant number, since it is smaller than the sum of its proper divisors (180023796).

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

81231660 is a wasteful number, since it uses less digits than its factorization.

81231660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1285 (or 1274 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 81231660 is about 9012.8608110855. The cubic root of 81231660 is about 433.0869618588.

Adding to 81231660 its reverse (6613218), we get a palindrome (87844878).

The spelling of 81231660 in words is "eighty-one million, two hundred thirty-one thousand, six hundred sixty".