81171540 has 72 divisors (see below), whose sum is σ = 248812200. Its totient is φ = 21417984.

The previous prime is 81171529. The next prime is 81171581. The reversal of 81171540 is 4517118.

81171540 is a `hidden beast` number, since 8 + 117 + 1 + 540 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 27060804 + 54110736 = 5202^2 + 7356^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 15136 + ... + 19784.

It is an arithmetic number, because the mean of its divisors is an integer number (3455725).

Almost surely, 2^81171540 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 81171540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (124406100).

81171540 is an abundant number, since it is smaller than the sum of its proper divisors (167640660).

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

81171540 is a wasteful number, since it uses less digits than its factorization.

81171540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4761 (or 4756 counting only the distinct ones).

The product of its (nonzero) digits is 1120, while the sum is 27.

The square root of 81171540 is about 9009.5249597301. The cubic root of 81171540 is about 432.9800921391.

Adding to 81171540 its reverse (4517118), we get a palindrome (85688658).

The spelling of 81171540 in words is "eighty-one million, one hundred seventy-one thousand, five hundred forty".