81213500 has 48 divisors (see below), whose sum is σ = 180442080. Its totient is φ = 31923200.

The previous prime is 81213491. The next prime is 81213523. The reversal of 81213500 is 531218.

It is a Harshad number since it is a multiple of its sum of digits (20).

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, 28124 + ... + 30876.

It is an arithmetic number, because the mean of its divisors is an integer number (3759210).

Almost surely, 2^81213500 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 81213500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (90221040).

81213500 is an abundant number, since it is smaller than the sum of its proper divisors (99228580).

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

81213500 is a wasteful number, since it uses less digits than its factorization.

81213500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2831 (or 2819 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 20.

The square root of 81213500 is about 9011.8533055083. The cubic root of 81213500 is about 433.0546860795.

Adding to 81213500 its reverse (531218), we get a palindrome (81744718).

The spelling of 81213500 in words is "eighty-one million, two hundred thirteen thousand, five hundred".