81771720944 has 80 divisors (see below), whose sum is σ = 172435168800. Its totient is φ = 37408407552.

The previous prime is 81771720941. The next prime is 81771720977. The reversal of 81771720944 is 44902717718.

It is a super-2 number, since 2×81771720944² (a number of 23 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81771720892 and 81771720901.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81771720941) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 14680592 + ... + 14686160.

It is an arithmetic number, because the mean of its divisors is an integer number (2155439610).

Almost surely, 2^81771720944 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 81771720944, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (86217584400).

81771720944 is an abundant number, since it is smaller than the sum of its proper divisors (90663447856).

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

81771720944 is a wasteful number, since it uses less digits than its factorization.

81771720944 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7090 (or 7084 counting only the distinct ones).

The product of its (nonzero) digits is 790272, while the sum is 50.

The spelling of 81771720944 in words is "eighty-one billion, seven hundred seventy-one million, seven hundred twenty thousand, nine hundred forty-four".