81005739840 has 672 divisors, whose sum is σ = 306776774304. Its totient is φ = 19534970880.

The previous prime is 81005739833. The next prime is 81005739851. The reversal of 81005739840 is 4893750018.

It can be written as a sum of positive squares in 16 ways, for example, as 3378864384 + 77626875456 = 58128^2 + 278616^2 .

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 175717210 + ... + 175717670.

It is an arithmetic number, because the mean of its divisors is an integer number (456513057).

Almost surely, 2^81005739840 is an apocalyptic number.

81005739840 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 81005739840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (153388387152).

81005739840 is an abundant number, since it is smaller than the sum of its proper divisors (225771034464).

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

81005739840 is a wasteful number, since it uses less digits than its factorization.

81005739840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 635 (or 622 counting only the distinct ones).

The product of its (nonzero) digits is 241920, while the sum is 45.

The spelling of 81005739840 in words is "eighty-one billion, five million, seven hundred thirty-nine thousand, eight hundred forty".