81691488 has 72 divisors (see below), whose sum is σ = 244553400. Its totient is φ = 25795584.

The previous prime is 81691487. The next prime is 81691501. The reversal of 81691488 is 88419618.

81691488 is a `hidden beast` number, since 8 + 169 + 1 + 488 = 666.

It is a tau number, because it is divible by the number of its divisors (72).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81691487) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1993 + ... + 12936.

It is an arithmetic number, because the mean of its divisors is an integer number (3396575).

Almost surely, 2^81691488 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 81691488, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (122276700).

81691488 is an abundant number, since it is smaller than the sum of its proper divisors (162861912).

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

81691488 is a wasteful number, since it uses less digits than its factorization.

81691488 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14964 (or 14953 counting only the distinct ones).

The product of its digits is 110592, while the sum is 45.

The square root of 81691488 is about 9038.3343598254. The cubic root of 81691488 is about 433.9026164167.

The spelling of 81691488 in words is "eighty-one million, six hundred ninety-one thousand, four hundred eighty-eight".