81323640 has 96 divisors (see below), whose sum is σ = 265749120. Its totient is φ = 21567744.

The previous prime is 81323609. The next prime is 81323647. The reversal of 81323640 is 4632318.

It is a happy number.

81323640 is a `hidden beast` number, since 8 + 13 + 2 + 3 + 640 = 666.

It is a super-2 number, since 2×81323640² = 13227068845699200, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81323647) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 79774 + ... + 80786.

It is an arithmetic number, because the mean of its divisors is an integer number (2768220).

Almost surely, 2^81323640 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81323640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (132874560).

81323640 is an abundant number, since it is smaller than the sum of its proper divisors (184425480).

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

81323640 is a wasteful number, since it uses less digits than its factorization.

81323640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1253 (or 1246 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 81323640 is about 9017.9620757686. The cubic root of 81323640 is about 433.2503641283.

Adding to 81323640 its reverse (4632318), we get a palindrome (85955958).

The spelling of 81323640 in words is "eighty-one million, three hundred twenty-three thousand, six hundred forty".