81641649600 has 840 divisors, whose sum is σ = 354150094848. Its totient is φ = 18052761600.

The previous prime is 81641649589. The next prime is 81641649647. The reversal of 81641649600 is 694614618.

It is a tau number, because it is divible by the number of its divisors (840).

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 119 ways as a sum of consecutive naturals, for example, 28121749 + ... + 28124651.

Almost surely, 2^81641649600 is an apocalyptic number.

81641649600 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81641649600, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (177075047424).

81641649600 is an abundant number, since it is smaller than the sum of its proper divisors (272508445248).

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

81641649600 is a wasteful number, since it uses less digits than its factorization.

81641649600 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2975 (or 2951 counting only the distinct ones).

The product of its (nonzero) digits is 248832, while the sum is 45.

The spelling of 81641649600 in words is "eighty-one billion, six hundred forty-one million, six hundred forty-nine thousand, six hundred".