81988640 has 24 divisors (see below), whose sum is σ = 193698540. Its totient is φ = 32795392.

The previous prime is 81988639. The next prime is 81988651. The reversal of 81988640 is 4688918.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 76247824 + 5740816 = 8732^2 + 2396^2 .

It is a junction number, because it is equal to n+sod(n) for n = 81988591 and 81988600.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 256055 + ... + 256374.

Almost surely, 2^81988640 is an apocalyptic number.

81988640 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81988640 is an abundant number, since it is smaller than the sum of its proper divisors (111709900).

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

81988640 is a wasteful number, since it uses less digits than its factorization.

81988640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 512444 (or 512436 counting only the distinct ones).

The product of its (nonzero) digits is 110592, while the sum is 44.

The square root of 81988640 is about 9054.7578653435. The cubic root of 81988640 is about 434.4280853293.

It can be divided in two parts, 81988 and 640, that added together give a palindrome (82628).

The spelling of 81988640 in words is "eighty-one million, nine hundred eighty-eight thousand, six hundred forty".