81209640780 has 216 divisors, whose sum is σ = 261392367600. Its totient is φ = 20351948544.

The previous prime is 81209640779. The next prime is 81209640793. The reversal of 81209640780 is 8704690218.

81209640780 is a `hidden beast` number, since 81 + 2 + 0 + 96 + 407 + 80 = 666.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 66077206 + ... + 66078434.

It is an arithmetic number, because the mean of its divisors is an integer number (1210149850).

Almost surely, 2^81209640780 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81209640780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (130696183800).

81209640780 is an abundant number, since it is smaller than the sum of its proper divisors (180182726820).

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

81209640780 is a wasteful number, since it uses less digits than its factorization.

81209640780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1541 (or 1397 counting only the distinct ones).

The product of its (nonzero) digits is 193536, while the sum is 45.

The spelling of 81209640780 in words is "eighty-one billion, two hundred nine million, six hundred forty thousand, seven hundred eighty".