My code below works but I an looking to speed it up to apply to large arrays. I have large integers and I want to store the exponent and first and last few digits.

nelems := 10;  ~ takes about 50mins when n=100,000,000
n := 374894756873546859847556;
op(n);
A := Array(1 .. 4, 1 .. nelems);
length(n);
st := time();
for i to nelems do
    A[1, i] := i^10*n;
    A[2, i] := length(A[1, i]) - 1;
    b := convert(A[1, i], string);
    A[3, i] := parse(b[1 .. 3]);
    A[4, i] := parse(b[-3 .. -1]);
end do;
time() - st;
A;
A[1, -2];
A[2, -2];
A[3, -2];
A[4, -2];

How do I remove Array B from Array A? e.g.

A:=Array([1,2,3,4,5,6,7,8...1000]
B:=Array([3,6,9,12,15....])   assuming A contains all the elements of B.

to get [1,2,4,5,7,8,11....]

Also is it possible to do it in place?

.I am testing out the MutableSet command, There seems to be a problem with the number of emements that can be operated on. When N =100000 things are ok. When N=1000000 (or there abouts) the process doesn't terminate last line. Uorks ok for sets. Using Maple 2018.2 on Win10 64bit.

Download Mutable_set_issue.mw

I have 2 questions here

1st I want to extend this set Ug3 := {1, 19, 23, 29} by repeatively subtracting 6 fron its elements. first pass should give

Ug3 := (Ug3-~ 6) union Ug3  Ug3 := {-5, 1, 13, 17, 19, 23, 29}

Now I dont want to add any elenments less than 6 so -5 need to go

Second pass produces

Ug3 := (Ug3-~ 6) union Ug3                Ug3 := {-11, -5, 1, 7, 11, 13, 17, 19, 23, 29}

Obiviously no elements less than 6 to be added on second pass either.

At this point there is no further elements that could be added to the set.

I am looking for an efficient method. I can use For loops and if then checks. The sets grow in length quickly. Repetition lengths are 6, 30 210, 2310,... I use sets because the numbers get ordered automaticially. Are sets efficient or should I use some form of table?
 

This should be simple but I am missing something. I want to sum the product of combinations of numbers.

I know I can assign values to a0...a[n-1]. But that isn't nice.

(n,k):= (5,4);
add(mul~(combinat:-choose([a(||)[](0..n-1)], k))) ; =a0*a1*a2*a3+a0*a1*a2*a4+a0*a1*a3*a4+a0*a2*a3*a4+a1*a2*a3*a4  which is correct.
add(mul~(combinat:-choose([(0..n-1)], k))) ;   #should be 24 but I get 0