81638520 has 32 divisors (see below), whose sum is σ = 244915920. Its totient is φ = 21770240.

The previous prime is 81638519. The next prime is 81638533. The reversal of 81638520 is 2583618.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 340041 + ... + 340280.

Almost surely, 2^81638520 is an apocalyptic number.

It is an amenable number.

81638520 is an abundant number, since it is smaller than the sum of its proper divisors (163277400).

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

81638520 is a wasteful number, since it uses less digits than its factorization.

81638520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 680335 (or 680331 counting only the distinct ones).

The product of its (nonzero) digits is 11520, while the sum is 33.

The square root of 81638520 is about 9035.4036987840. The cubic root of 81638520 is about 433.8088166690.

The spelling of 81638520 in words is "eighty-one million, six hundred thirty-eight thousand, five hundred twenty".