For example i have a sequence of sequence:
A = {{1,2,3},{4,5,6},{7,8,9}}

How do i write it if i want to say the 2nd element of the 3rd element in the sequence of sequence ? In this case the 2nd element of the 3rd element is 8.

I know that to write the nth element of sequence , i write it as A1 A2 A3 ect , but i tried to search on internet but cant find anything about this.

  • 1
    $\begingroup$ If it is finite mabe you could consider $A$ as a matrix and then write $A_{i,j}$ where $i$ is the $i$-th line and $j$ the column ? In your case the 2nd element of the 3rd element would be $A_{3,2} = 8$. $\endgroup$
    – Leo
    Sep 13, 2021 at 8:49
  • $\begingroup$ The $y$-th element (AKA ordered triple) of the sequence will contain the numbers $(3y-2, 3y-1, 3y).$ $\endgroup$ Sep 13, 2021 at 8:49
  • $\begingroup$ @Leo ah ! i didnt thought about that , thanks you are right maybe i can consider it as matrix . I'm sorry but i'm a beginner at math , can you please write an answer on how to write it using matrix ? $\endgroup$ Sep 13, 2021 at 8:51
  • $\begingroup$ @i'mashamedwithwhatiasked I don't have sufficient information about your problem. But making the assumption that your sequence is only compose of triplet of point, i.e. $A=\{\{1,2,3\},..,\{7,8,9\},\{10,11,12\},...\}$ The $n$-th triple is given (as said by @user2661923) ($3n-2,3n-1,3n$). So the $i$-th element of the $n$-th sequence would be $A_{i, n}$ $\endgroup$
    – Leo
    Sep 13, 2021 at 8:57

1 Answer 1


$n-th$ element is equal to a triple $(3n-2, 3n -1, 3n )$


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