81344640 has 128 divisors (see below), whose sum is σ = 279316800. Its totient is φ = 20017152.

The previous prime is 81344621. The next prime is 81344689. The reversal of 81344640 is 4644318.

It is a tau number, because it is divible by the number of its divisors (128).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 81344598 and 81344607.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 23331 + ... + 26589.

Almost surely, 2^81344640 is an apocalyptic number.

81344640 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 81344640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (139658400).

81344640 is an abundant number, since it is smaller than the sum of its proper divisors (197972160).

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

81344640 is a wasteful number, since it uses less digits than its factorization.

81344640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3294 (or 3282 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 30.

The square root of 81344640 is about 9019.1263434991. The cubic root of 81344640 is about 433.2876533044.

Adding to 81344640 its reverse (4644318), we get a palindrome (85988958).

The spelling of 81344640 in words is "eighty-one million, three hundred forty-four thousand, six hundred forty".