A249484 Sequence which reappears when consecutive terms are erased iff they have the same parity.

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

Offset

0,2

Links

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000

Éric Angelini, More fractal triangles, SeqFan list, Jan 12 2015.

Example

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

Prog

(Haskell)
a249484 n = a249484_list !! n
a249484_list = 1 : concat (zipWith (++) ([2] : f [5, 2, 7]) (f [4, 3])) where
   f = iterate (\row -> [g $ head row] ++ row ++ [g $ last row])
   g x = x + ((5 -) . (* 2) . flip mod 2) x

Crossrefs

Cf. A249900.

Sequence in context: A011387 A019656 A256751 * A134017 A292285 A163984

Adjacent sequences: A249481 A249482 A249483 * A249485 A249486 A249487

Keyword

nonn

Author

Eric Angelini and Reinhard Zumkeller, Jan 13 2015

Status

approved