81336640 has 112 divisors (see below), whose sum is σ = 241547904. Its totient is φ = 25344000.

The previous prime is 81336637. The next prime is 81336641. The reversal of 81336640 is 4663318.

It is a tau number, because it is divible by the number of its divisors (112).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81336641) 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, 22990 + ... + 26290.

Almost surely, 2^81336640 is an apocalyptic number.

81336640 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81336640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (120773952).

81336640 is an abundant number, since it is smaller than the sum of its proper divisors (160211264).

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

81336640 is a wasteful number, since it uses less digits than its factorization.

81336640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3336 (or 3326 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 31.

The square root of 81336640 is about 9018.6828306577. The cubic root of 81336640 is about 433.2734486608.

Adding to 81336640 its reverse (4663318), we get a palindrome (85999958).

The spelling of 81336640 in words is "eighty-one million, three hundred thirty-six thousand, six hundred forty".