81972840 has 128 divisors (see below), whose sum is σ = 261648000. Its totient is φ = 20487168.

The previous prime is 81972833. The next prime is 81972853. The reversal of 81972840 is 4827918.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 357846 + ... + 358074.

It is an arithmetic number, because the mean of its divisors is an integer number (2044125).

Almost surely, 2^81972840 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 81972840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (130824000).

81972840 is an abundant number, since it is smaller than the sum of its proper divisors (179675160).

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

81972840 is a wasteful number, since it uses less digits than its factorization.

81972840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 419 (or 415 counting only the distinct ones).

The product of its (nonzero) digits is 32256, while the sum is 39.

The square root of 81972840 is about 9053.8853538136. The cubic root of 81972840 is about 434.4001773789.

The spelling of 81972840 in words is "eighty-one million, nine hundred seventy-two thousand, eight hundred forty".