Facebook task solution http://habrahabr.ru/post/210796/

facebook.erl

-module(facebook).
-export([square/1, print_square/1]).

square(N)->square(1, N).
square(Start, 1)->[[Start]];
square(Start, 2)->[[Start, Start+1], [Start+3, Start+2]];
square(Start, N)->
    TopRight = Start+N-1,
    [lists:seq(Start, TopRight)]++
    extend(square(TopRight+3*N-3, N-2), TopRight+3*N-4, TopRight+1, [])++
    [lists:reverse(lists:seq(TopRight+N-1, TopRight+2*N-2))].

extend([H|T], Left, Right, Acc)->
    extend(T, Left-1, Right+1, [[Left]++H++[Right]|Acc]);
extend([], _, _, Acc)->lists:reverse(Acc).

print_square(N)->
    lists:foreach(fun(Row)->io:format("~w~n", [Row]) end, square(N)).