81917640 has 96 divisors (see below), whose sum is σ = 304274880. Its totient is φ = 18723456.

The previous prime is 81917639. The next prime is 81917657. The reversal of 81917640 is 4671918.

81917640 is a `hidden beast` number, since 8 + 1 + 9 + 1 + 7 + 640 = 666.

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 = 81917595 and 81917604.

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, 13734 + ... + 18773.

It is an arithmetic number, because the mean of its divisors is an integer number (3169530).

Almost surely, 2^81917640 is an apocalyptic number.

It is an amenable number.

81917640 is an abundant number, since it is smaller than the sum of its proper divisors (222357240).

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

81917640 is a wasteful number, since it uses less digits than its factorization.

81917640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32531 (or 32524 counting only the distinct ones).

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

The square root of 81917640 is about 9050.8364254360. The cubic root of 81917640 is about 434.3026480256.

The spelling of 81917640 in words is "eighty-one million, nine hundred seventeen thousand, six hundred forty".