81243840 has 56 divisors (see below), whose sum is σ = 257952240. Its totient is φ = 21664768.

The previous prime is 81243793. The next prime is 81243847. The reversal of 81243840 is 4834218.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 81243798 and 81243807.

It is not an unprimeable number, because it can be changed into a prime (81243847) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 41355 + ... + 43274.

It is an arithmetic number, because the mean of its divisors is an integer number (4606290).

Almost surely, 2^81243840 is an apocalyptic number.

81243840 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81243840 is an abundant number, since it is smaller than the sum of its proper divisors (176708400).

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

81243840 is a wasteful number, since it uses less digits than its factorization.

81243840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 84649 (or 84639 counting only the distinct ones).

The product of its (nonzero) digits is 6144, while the sum is 30.

The square root of 81243840 is about 9013.5364868624. The cubic root of 81243840 is about 433.1086066853.

The spelling of 81243840 in words is "eighty-one million, two hundred forty-three thousand, eight hundred forty".