writing an integer variable with vector of variable size with appending

for i = 1:N

A= [a11 a12 a13 ...] % size is variable

   % I want it should write in the file in this format
   fprintf("i is A\n")
   % e.g 1 is 2 3 5
   %     2 is 5 8 9 10 12
   %     and so on ...
end

please tell me the format for it

[sixwwwwww]

Dear Tinkle, Can you please clear the sequence of numbers which you want to be written in file?