81621256320 has 192 divisors, whose sum is σ = 291567907800. Its totient is φ = 21015085056.

The previous prime is 81621256247. The next prime is 81621256393. The reversal of 81621256320 is 2365212618.

81621256320 is a `hidden beast` number, since 8 + 1 + 6 + 2 + 12 + 5 + 632 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (81621256247) and next prime (81621256393).

It can be written as a sum of positive squares in 4 ways, for example, as 61929308736 + 19691947584 = 248856^2 + 140328^2 .

It is a tau number, because it is divible by the number of its divisors (192).

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

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 77277 + ... + 411356.

Almost surely, 2^81621256320 is an apocalyptic number.

81621256320 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 81621256320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (145783953900).

81621256320 is an abundant number, since it is smaller than the sum of its proper divisors (209946651480).

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

81621256320 is a wasteful number, since it uses less digits than its factorization.

81621256320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 488687 (or 488672 counting only the distinct ones).

The product of its (nonzero) digits is 34560, while the sum is 36.

Adding to 81621256320 its reverse (2365212618), we get a palindrome (83986468938).

The spelling of 81621256320 in words is "eighty-one billion, six hundred twenty-one million, two hundred fifty-six thousand, three hundred twenty".