A220424 Triangle read by rows: A007651 expanded into single digits.

1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 2, 1, 1, 1, 1, 1, 2, 2, 1, 3, 1, 2, 2, 2, 1, 1, 3, 1, 1, 1, 2, 3, 1, 2, 3, 1, 1, 1, 1, 2, 2, 1, 3, 1, 1, 1, 2, 1, 3, 1, 1, 3, 1, 1, 2, 2, 1, 1, 3, 1, 1, 3, 2, 1, 1, 1, 3, 1, 1, 2, 3, 1, 1, 2, 2, 2, 1, 2, 3, 1, 1, 2, 3, 1, 2

Offset: 1

Author

Reinhard Zumkeller, Dec 15 2012

Keywords

• nonn
• base
• tabf

Comments

A007651(n) = sum{T(n,k)*10^(A005341(n)-k): k=1..A005341(n)}.

Examples

			.  Initial rows                          A007651
.  1:  1                                           1
.  2:  1,1                                        11
.  3:  1,2                                        12
.  4:  1,1,2,1                                  1121
.  5:  1,2,2,1,1,1                            122111
.  6:  1,1,2,2,1,3                            112213
.  7:  1,2,2,2,1,1,3,1                      12221131
.  8:  1,1,2,3,1,2,3,1,1,1                1123123111
.  9:  1,2,2,1,3,1,1,1,2,1,3,1,1,3    12213111213113 .
		

Links

• Reinhard Zumkeller, Rows n = 1..25 of triangle, flattened
• Eric Weisstein's World of Mathematics, Look and Say Sequence
• Wikipedia, Look-and-say sequence

Crossrefs

Cf. A005341 (row lengths), A034002 (method A version).

Programs

Haskell

import Data.List (group)
a220424 n k = a220424_tabf !! (n-1) !! (k-1)
a220424_row n = a220424_tabf !! (n-1)
a220424_tabf = iterate
               (concatMap (\xs -> [head xs, length xs]) . group) [1]