81618840 has 144 divisors (see below), whose sum is σ = 276335280. Its totient is φ = 21695040.

The previous prime is 81618839. The next prime is 81618841. The reversal of 81618840 is 4881618.

It is an interprime number because it is at equal distance from previous prime (81618839) and next prime (81618841).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 81618795 and 81618804.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81618841) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 262285 + ... + 262595.

It is an arithmetic number, because the mean of its divisors is an integer number (1918995).

Almost surely, 2^81618840 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 81618840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (138167640).

81618840 is an abundant number, since it is smaller than the sum of its proper divisors (194716440).

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

81618840 is an equidigital number, since it uses as much as digits as its factorization.

81618840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 346 (or 321 counting only the distinct ones).

The product of its (nonzero) digits is 12288, while the sum is 36.

The square root of 81618840 is about 9034.3145838519. The cubic root of 81618840 is about 433.7739554963.

The spelling of 81618840 in words is "eighty-one million, six hundred eighteen thousand, eight hundred forty".