81549206640 has 960 divisors, whose sum is σ = 326409108480. Its totient is φ = 18044928000.

The previous prime is 81549206593. The next prime is 81549206657. The reversal of 81549206640 is 4660294518.

81549206640 is a `hidden beast` number, since 8 + 1 + 549 + 2 + 0 + 66 + 40 = 666.

It is a super-2 number, since 2×81549206640² (a number of 23 digits) contains 22 as substring.

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 191 ways as a sum of consecutive naturals, for example, 455582071 + ... + 455582249.

It is an arithmetic number, because the mean of its divisors is an integer number (340009488).

Almost surely, 2^81549206640 is an apocalyptic number.

81549206640 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 81549206640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (163204554240).

81549206640 is an abundant number, since it is smaller than the sum of its proper divisors (244859901840).

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

81549206640 is a wasteful number, since it uses less digits than its factorization.

81549206640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 334 (or 325 counting only the distinct ones).

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

The spelling of 81549206640 in words is "eighty-one billion, five hundred forty-nine million, two hundred six thousand, six hundred forty".