OFFSET
0,3
COMMENTS
LINKS
Reinhard Zumkeller, Rows n = 0..100 of triangle, flattened
Éric Angelini, More (and more) fractal trees - and erasures, SeqFan list, Jan 08 2015.
FORMULA
T(n,0) = 0; T(n,1)=1; T(n,2*n-1) = 2; T(n+1,k+2) = T(n,k)+3, k = 0..3*n-1.
EXAMPLE
. 0: | 0 1 2|
. 1: 0 1 | 3 4 5| 2
. 2: 0 1 3 4 | 6 7 8| 5 2
. 3: 0 1 3 4 6 7 | 9 10 11| 8 5 2
. 4: 0 1 3 4 6 7 9 10 |12 13 14| 11 8 5 2
. 5: 0 1 3 4 6 7 9 10 12 13 |15 16 17| 14 11 8 5 2
. 6: 0 1 3 4 6 7 9 10 12 13 15 16 |18 19 20| 17 14 11 8 5 2
. 7: 0 1 3 4 6 7 9 10 12 13 15 16 18 19 |21 22 23| 20 17 14 11 8 5 2 .
PROG
(Haskell)
a253672 n k = a253672_tabf !! n !! k
a253672_row n = a253672_tabf !! n
a253672_tabf = [0, 1, 2] : f [] [0, 1, 2] [] (iterate (map (+ 3)) [3..5]) where
f as bs cs (uvws:uvwss) = (as' ++ uvws ++ cs') : f as' uvws cs' uvwss
where as' = as ++ [u, v]; cs' = [w] ++ cs
[u, v, w] = bs
a253672_list = concat a253672_tabf
CROSSREFS
KEYWORD
nonn,tabf
AUTHOR
Eric Angelini and Reinhard Zumkeller, Jan 08 2015
STATUS
approved