81213240 has 64 divisors (see below), whose sum is σ = 249321600. Its totient is φ = 21151872.

The previous prime is 81213229. The next prime is 81213263. The reversal of 81213240 is 4231218.

It is a congruent number.

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, 2710 + ... + 13029.

It is an arithmetic number, because the mean of its divisors is an integer number (3895650).

Almost surely, 2^81213240 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 81213240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (124660800).

81213240 is an abundant number, since it is smaller than the sum of its proper divisors (168108360).

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

81213240 is a wasteful number, since it uses less digits than its factorization.

81213240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15796 (or 15792 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 21.

The square root of 81213240 is about 9011.8388800511. The cubic root of 81213240 is about 433.0542239464.

Adding to 81213240 its reverse (4231218), we get a palindrome (85444458).

The spelling of 81213240 in words is "eighty-one million, two hundred thirteen thousand, two hundred forty".