81851440 has 80 divisors (see below), whose sum is σ = 212129280. Its totient is φ = 29116160.

The previous prime is 81851423. The next prime is 81851443. The reversal of 81851440 is 4415818.

It is a tau number, because it is divible by the number of its divisors (80).

It is not an unprimeable number, because it can be changed into a prime (81851443) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 40371 + ... + 42349.

It is an arithmetic number, because the mean of its divisors is an integer number (2651616).

Almost surely, 2^81851440 is an apocalyptic number.

81851440 is a gapful number since it is divisible by the number (80) 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 81851440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (106064640).

81851440 is an abundant number, since it is smaller than the sum of its proper divisors (130277840).

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

81851440 is a wasteful number, since it uses less digits than its factorization.

81851440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2050 (or 2044 counting only the distinct ones).

The product of its (nonzero) digits is 5120, while the sum is 31.

The square root of 81851440 is about 9047.1785657187. The cubic root of 81851440 is about 434.1856256782.

It can be divided in two parts, 81 and 851440, that multiplied together give a triangular number (68966640 = T₁₁₇₄₄).

The spelling of 81851440 in words is "eighty-one million, eight hundred fifty-one thousand, four hundred forty".