81694640 has 20 divisors (see below), whose sum is σ = 189940224. Its totient is φ = 32677824.

The previous prime is 81694637. The next prime is 81694649. The reversal of 81694640 is 4649618.

It is a tau number, because it is divible by the number of its divisors (20).

It is a junction number, because it is equal to n+sod(n) for n = 81694594 and 81694603.

It is not an unprimeable number, because it can be changed into a prime (81694649) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 510512 + ... + 510671.

Almost surely, 2^81694640 is an apocalyptic number.

81694640 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81694640 is an abundant number, since it is smaller than the sum of its proper divisors (108245584).

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

81694640 is a wasteful number, since it uses less digits than its factorization.

81694640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1021196 (or 1021190 counting only the distinct ones).

The product of its (nonzero) digits is 41472, while the sum is 38.

The square root of 81694640 is about 9038.5087265544. The cubic root of 81694640 is about 433.9081969387.

The spelling of 81694640 in words is "eighty-one million, six hundred ninety-four thousand, six hundred forty".