81961943040 has 420 divisors, whose sum is σ = 295371135444. Its totient is φ = 21743271936.

The previous prime is 81961943033. The next prime is 81961943069. The reversal of 81961943040 is 4034916918.

81961943040 is a `hidden beast` number, since 81 + 96 + 19 + 430 + 40 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 24546115584 + 57415827456 = 156672^2 + 239616^2 .

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 19 ways as a sum of consecutive naturals, for example, 424673184 + ... + 424673376.

Almost surely, 2^81961943040 is an apocalyptic number.

81961943040 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 81961943040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (147685567722).

81961943040 is an abundant number, since it is smaller than the sum of its proper divisors (213409192404).

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

81961943040 is an frugal number, since it uses more digits than its factorization.

81961943040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 250 (or 203 counting only the distinct ones).

The product of its (nonzero) digits is 186624, while the sum is 45.

The spelling of 81961943040 in words is "eighty-one billion, nine hundred sixty-one million, nine hundred forty-three thousand, forty".