81684998640 has 1280 divisors, whose sum is σ = 365016637440. Its totient is φ = 16349921280.

The previous prime is 81684998621. The next prime is 81684998641. The reversal of 81684998640 is 4689948618.

81684998640 is a `hidden beast` number, since 8 + 1 + 68 + 499 + 86 + 4 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81684998641) by changing a digit.

It is a polite number, since it can be written in 255 ways as a sum of consecutive naturals, for example, 242388552 + ... + 242388888.

It is an arithmetic number, because the mean of its divisors is an integer number (285169248).

Almost surely, 2^81684998640 is an apocalyptic number.

81684998640 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 81684998640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (182508318720).

81684998640 is an abundant number, since it is smaller than the sum of its proper divisors (283331638800).

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

81684998640 is a wasteful number, since it uses less digits than its factorization.

81684998640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 447 (or 435 counting only the distinct ones).

The product of its (nonzero) digits is 23887872, while the sum is 63.

The spelling of 81684998640 in words is "eighty-one billion, six hundred eighty-four million, nine hundred ninety-eight thousand, six hundred forty".