81917742438 has 144 divisors (see below), whose sum is σ = 213179226624. Its totient is φ = 22653146880.

The previous prime is 81917742409. The next prime is 81917742493. The reversal of 81917742438 is 83424771918.

81917742438 is a `hidden beast` number, since 8 + 19 + 177 + 424 + 38 = 666.

It is a super-2 number, since 2×81917742438² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

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, 4583656 + ... + 4601492.

It is an arithmetic number, because the mean of its divisors is an integer number (1480411296).

Almost surely, 2^81917742438 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81917742438, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (106589613312).

81917742438 is an abundant number, since it is smaller than the sum of its proper divisors (131261484186).

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

81917742438 is a wasteful number, since it uses less digits than its factorization.

81917742438 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18027 (or 18017 counting only the distinct ones).

The product of its digits is 2709504, while the sum is 54.

The spelling of 81917742438 in words is "eighty-one billion, nine hundred seventeen million, seven hundred forty-two thousand, four hundred thirty-eight".