81072640 has 80 divisors (see below), whose sum is σ = 212129280. Its totient is φ = 29470720.

The previous prime is 81072617. The next prime is 81072647. The reversal of 81072640 is 4627018.

81072640 = 1187² + 1188² + ... + 1241².

It is a tau number, because it is divible by the number of its divisors (80).

It is a zygodrome in base 14.

It is a junction number, because it is equal to n+sod(n) for n = 81072599 and 81072608.

It is not an unprimeable number, because it can be changed into a prime (81072647) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 26721 + ... + 29599.

It is an arithmetic number, because the mean of its divisors is an integer number (2651616).

Almost surely, 2^81072640 is an apocalyptic number.

81072640 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 81072640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (106064640).

81072640 is an abundant number, since it is smaller than the sum of its proper divisors (131056640).

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

81072640 is a wasteful number, since it uses less digits than its factorization.

81072640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2913 (or 2897 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 28.

The square root of 81072640 is about 9004.0346511994. The cubic root of 81072640 is about 432.8041719650.

Adding to 81072640 its reverse (4627018), we get a palindrome (85699658).

The spelling of 81072640 in words is "eighty-one million, seventy-two thousand, six hundred forty".