%I #12 Jan 02 2023 12:30:51

%S 1,2,4,3,5,2,7,9,4,3,6,8,5,2,7,10,12,9,4,3,6,11,13,8,5,2,7,10,15,17,

%T 12,9,4,3,6,11,14,16,13,8,5,2,7,10,15,18,20,17,12,9,4,3,6,11,14,19,21,

%U 16,13,8,5,2,7,10,15,18,23,25,20,17,12,9,4,3,6

%N Sequence which reappears when consecutive terms are erased iff they have the same parity.

%H Reinhard Zumkeller, <a href="/A249484/b249484.txt">Table of n, a(n) for n = 0..10000</a>

%H Éric Angelini, <a href="http://list.seqfan.eu/oldermail/seqfan/2015-January/014291.html">More fractal triangles</a>, SeqFan list, Jan 12 2015.

%e . n : 0|1|2|3|4|5|6|7|8|9|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|

%e . a(n): 1 2 4 3 5 2 7 9 4 3 6 8 5 2 7 10 12 9 4 3 6 11 13 8 5

%e . 0/1 : 1 0 0 1 1 0 1 1 0 1 0 0 1 0 1 0 0 1 0 1 0 1 1 0 1

%e . : 1 _ _ _ _ 2 _ _ 4 3 _ _ 5 2 7 _ _ 9 4 3 6 _ _ 8 5 .

%o (Haskell)

%o a249484 n = a249484_list !! n

%o a249484_list = 1 : concat (zipWith (++) ([2] : f [5,2,7]) (f [4,3])) where

%o f = iterate (\row -> [g $ head row] ++ row ++ [g $ last row])

%o g x = x + ((5 -) . (* 2) . flip mod 2) x

%Y Cf. A249900.

%K nonn

%O 0,2

%A _Eric Angelini_ and _Reinhard Zumkeller_, Jan 13 2015