81537500 has 72 divisors (see below), whose sum is σ = 194893776. Its totient is φ = 29600000.

The previous prime is 81537499. The next prime is 81537517. The reversal of 81537500 is 573518.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 137204 + ... + 137796.

It is an arithmetic number, because the mean of its divisors is an integer number (2706858).

Almost surely, 2^81537500 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 81537500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (97446888).

81537500 is an abundant number, since it is smaller than the sum of its proper divisors (113356276).

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

81537500 is a wasteful number, since it uses less digits than its factorization.

81537500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 633 (or 611 counting only the distinct ones).

The product of its (nonzero) digits is 4200, while the sum is 29.

The square root of 81537500 is about 9029.8117366864. The cubic root of 81537500 is about 433.6298102601.

The spelling of 81537500 in words is "eighty-one million, five hundred thirty-seven thousand, five hundred".