81171840 has 128 divisors (see below), whose sum is σ = 263013120. Its totient is φ = 21288960.

The previous prime is 81171829. The next prime is 81171851. The reversal of 81171840 is 4817118.

It is an interprime number because it is at equal distance from previous prime (81171829) and next prime (81171851).

It is a tau number, because it is divible by the number of its divisors (128).

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 = 81171798 and 81171807.

It is a congruent number.

It is an unprimeable number.

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, 128325 + ... + 128955.

It is an arithmetic number, because the mean of its divisors is an integer number (2054790).

Almost surely, 2^81171840 is an apocalyptic number.

81171840 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 81171840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (131506560).

81171840 is an abundant number, since it is smaller than the sum of its proper divisors (181841280).

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

81171840 is a wasteful number, since it uses less digits than its factorization.

81171840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 720 (or 708 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 30.

The square root of 81171840 is about 9009.5416087612. The cubic root of 81171840 is about 432.9806255521.

Adding to 81171840 its reverse (4817118), we get a palindrome (85988958).

The spelling of 81171840 in words is "eighty-one million, one hundred seventy-one thousand, eight hundred forty".