81616640 has 72 divisors (see below), whose sum is σ = 223450080. Its totient is φ = 27979776.

The previous prime is 81616637. The next prime is 81616651. The reversal of 81616640 is 4661618.

It is a happy number.

It is a super-2 number, since 2×81616640² = 13322551849779200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a junction number, because it is equal to n+sod(n) for n = 81616597 and 81616606.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4406 + ... + 13514.

Almost surely, 2^81616640 is an apocalyptic number.

81616640 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 81616640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (111725040).

81616640 is an abundant number, since it is smaller than the sum of its proper divisors (141833440).

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

81616640 is an equidigital number, since it uses as much as digits as its factorization.

81616640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9137 (or 9123 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 32.

The square root of 81616640 is about 9034.1928250398. The cubic root of 81616640 is about 433.7700580658.

The spelling of 81616640 in words is "eighty-one million, six hundred sixteen thousand, six hundred forty".