81645721600 has 72 divisors (see below), whose sum is σ = 202432082580. Its totient is φ = 32658268160.

The previous prime is 81645721513. The next prime is 81645721603. The reversal of 81645721600 is 612754618.

It is a Harshad number since it is a multiple of its sum of digits (40).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81645721603) 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 5 ways as a sum of consecutive naturals, for example, 746122 + ... + 848521.

Almost surely, 2^81645721600 is an apocalyptic number.

81645721600 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81645721600 is an abundant number, since it is smaller than the sum of its proper divisors (120786360980).

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

81645721600 is a wasteful number, since it uses less digits than its factorization.

81645721600 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1594675 (or 1594650 counting only the distinct ones).

The product of its (nonzero) digits is 80640, while the sum is 40.

The spelling of 81645721600 in words is "eighty-one billion, six hundred forty-five million, seven hundred twenty-one thousand, six hundred".