Ý tưởng: Viết hàm kiểm tra xem phần tử a[i] có dạng 3^k+2 hay không.
uses crt;
var b,j,i,x:integer;
a:array[1..100] of integer;
Function gt(k:integer):longint;
var j:integer;s:longint;
begin
s:=1;
for j:=1 to k do
s:=s*3;
gt:=s;
end;
{-------------------------------------}
Function kt(x:integer):boolean;
var i,j,k:integer;s:longint;
begin
kt:=false;
s:=1;
k:=0;
Repeat
inc(k);
gt(k);
Until gt(k)>=x-2;
if gt(k)=x-2 then kt:=true;
end;
{---------------------------------}
begin
clrscr;
Write('Nhap so phan tu= ');readln(x);
For i:=1 to x do begin
write('a[',i,']= ');
readln(a[i]);
end;
For i:=1 to x do
if kt(a[i]) then write(a[i],' ');writeln;
readln
end.
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