81209456640 has 288 divisors, whose sum is σ = 303112424160. Its totient is φ = 19989725184.

The previous prime is 81209456617. The next prime is 81209456663. The reversal of 81209456640 is 4665490218.

81209456640 is a `hidden beast` number, since 81 + 2 + 0 + 9 + 4 + 566 + 4 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (81209456617) and next prime (81209456663).

It is a tau number, because it is divible by the number of its divisors (288).

It is a hoax number, since the sum of its digits (45) coincides with the sum of the digits of its distinct prime factors.

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 23 ways as a sum of consecutive naturals, for example, 1164189 + ... + 1231971.

It is an arithmetic number, because the mean of its divisors is an integer number (1052473695).

Almost surely, 2^81209456640 is an apocalyptic number.

81209456640 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 81209456640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (151556212080).

81209456640 is an abundant number, since it is smaller than the sum of its proper divisors (221902967520).

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

81209456640 is a wasteful number, since it uses less digits than its factorization.

81209456640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 67829 (or 67806 counting only the distinct ones).

The product of its (nonzero) digits is 414720, while the sum is 45.

The spelling of 81209456640 in words is "eighty-one billion, two hundred nine million, four hundred fifty-six thousand, six hundred forty".