81531261504000 has 2400 divisors, whose sum is σ = 385413561149760. Its totient is φ = 16940980224000.

The previous prime is 81531261503929. The next prime is 81531261504041. The reversal of 81531261504000 is 40516213518.

81531261504000 is a `hidden beast` number, since 8 + 1 + 5 + 31 + 2 + 615 + 0 + 4 + 0 + 0 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (2400).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 239 ways as a sum of consecutive naturals, for example, 2794161411 + ... + 2794190589.

Almost surely, 2^{81531261504000} is an apocalyptic number.

81531261504000 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 81531261504000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (192706780574880).

81531261504000 is an abundant number, since it is smaller than the sum of its proper divisors (303882299645760).

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

81531261504000 is a wasteful number, since it uses less digits than its factorization.

81531261504000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29249 (or 29207 counting only the distinct ones).

The product of its (nonzero) digits is 28800, while the sum is 36.

Adding to 81531261504000 its reverse (40516213518), we get a palindrome (81571777717518).

The spelling of 81531261504000 in words is "eighty-one trillion, five hundred thirty-one billion, two hundred sixty-one million, five hundred four thousand".