81639988 has 48 divisors (see below), whose sum is σ = 155151360. Its totient is φ = 37497600.

The previous prime is 81639983. The next prime is 81640003. The reversal of 81639988 is 88993618.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81639983) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 262353 + ... + 262663.

It is an arithmetic number, because the mean of its divisors is an integer number (3232320).

Almost surely, 2^81639988 is an apocalyptic number.

It is an amenable number.

81639988 is a deficient number, since it is larger than the sum of its proper divisors (73511372).

81639988 is a wasteful number, since it uses less digits than its factorization.

81639988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 448 (or 446 counting only the distinct ones).

The product of its digits is 746496, while the sum is 52.

The square root of 81639988 is about 9035.4849344128. The cubic root of 81639988 is about 433.8114168612.

It can be divided in two parts, 816 and 39988, that added together give a palindrome (40804).

The spelling of 81639988 in words is "eighty-one million, six hundred thirty-nine thousand, nine hundred eighty-eight".