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A220424 Triangle read by rows: A007651 expanded into single digits. 4
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

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

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

EXAMPLE

.  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 .

PROG

(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]

CROSSREFS

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

Sequence in context: A326700 A050412 A307017 * A182907 A334745 A323231

Adjacent sequences:  A220421 A220422 A220423 * A220425 A220426 A220427

KEYWORD

nonn,base,tabf

AUTHOR

Reinhard Zumkeller, Dec 15 2012

STATUS

approved

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Last modified May 6 15:28 EDT 2021. Contains 343586 sequences. (Running on oeis4.)