81981656064 has 704 divisors, whose sum is σ = 306590161920. Its totient is φ = 21021327360.

The previous prime is 81981656059. The next prime is 81981656083. The reversal of 81981656064 is 46065618918.

81981656064 is a `hidden beast` number, since 8 + 1 + 9 + 8 + 16 + 560 + 64 = 666.

It is a tau number, because it is divible by the number of its divisors (704).

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a self number, because there is not a number n which added to its sum of digits gives 81981656064.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 206502714 + ... + 206503110.

Almost surely, 2^81981656064 is an apocalyptic number.

81981656064 is a gapful number since it is divisible by the number (84) 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 81981656064, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (153295080960).

81981656064 is an abundant number, since it is smaller than the sum of its proper divisors (224608505856).

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

81981656064 is a wasteful number, since it uses less digits than its factorization.

81981656064 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 541 (or 517 counting only the distinct ones).

The product of its (nonzero) digits is 2488320, while the sum is 54.

The spelling of 81981656064 in words is "eighty-one billion, nine hundred eighty-one million, six hundred fifty-six thousand, sixty-four".