81721360 has 40 divisors (see below), whose sum is σ = 217146816. Its totient is φ = 28018560.

The previous prime is 81721331. The next prime is 81721361. The reversal of 81721360 is 6312718.

It is a tau number, because it is divible by the number of its divisors (40).

It is a Harshad number since it is a multiple of its sum of digits (28).

It is not an unprimeable number, because it can be changed into a prime (81721361) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 72406 + ... + 73525.

Almost surely, 2^81721360 is an apocalyptic number.

81721360 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81721360 is an abundant number, since it is smaller than the sum of its proper divisors (135425456).

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

81721360 is a wasteful number, since it uses less digits than its factorization.

81721360 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 145951 (or 145945 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 81721360 is about 9039.9867256540. The cubic root of 81721360 is about 433.9554981375.

The spelling of 81721360 in words is "eighty-one million, seven hundred twenty-one thousand, three hundred sixty".