81691740 has 168 divisors, whose sum is σ = 277639488. Its totient is φ = 20062080.

The previous prime is 81691739. The next prime is 81691741. The reversal of 81691740 is 4719618.

It is an interprime number because it is at equal distance from previous prime (81691739) and next prime (81691741).

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 = 81691695 and 81691704.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81691741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 55 ways as a sum of consecutive naturals, for example, 189325 + ... + 189755.

It is an arithmetic number, because the mean of its divisors is an integer number (1652616).

Almost surely, 2^81691740 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 81691740, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (138819744).

81691740 is an abundant number, since it is smaller than the sum of its proper divisors (195947748).

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

81691740 is a wasteful number, since it uses less digits than its factorization.

81691740 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 471 (or 454 counting only the distinct ones).

The product of its (nonzero) digits is 12096, while the sum is 36.

The square root of 81691740 is about 9038.3483004363. The cubic root of 81691740 is about 433.9030625804.

The spelling of 81691740 in words is "eighty-one million, six hundred ninety-one thousand, seven hundred forty".