81681900 has 72 divisors (see below), whose sum is σ = 243984384. Its totient is φ = 21076800.

The previous prime is 81681883. The next prime is 81681907. The reversal of 81681900 is 918618.

It is a super-2 number, since 2×81681900² = 13343865575220000, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81681907) by changing a digit.

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 23 ways as a sum of consecutive naturals, for example, 4909 + ... + 13691.

It is an arithmetic number, because the mean of its divisors is an integer number (3388672).

Almost surely, 2^81681900 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 81681900, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (121992192).

81681900 is an abundant number, since it is smaller than the sum of its proper divisors (162302484).

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

81681900 is a wasteful number, since it uses less digits than its factorization.

81681900 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8831 (or 8824 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 33.

The square root of 81681900 is about 9037.8039367979. The cubic root of 81681900 is about 433.8856402659.

The spelling of 81681900 in words is "eighty-one million, six hundred eighty-one thousand, nine hundred".