A220424 - OEIS

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

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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: A050412 A374382 A307017 * A182907 A334745 A323231

Adjacent sequences: A220421 A220422 A220423 * A220425 A220426 A220427

KEYWORD

nonn,base,tabf

AUTHOR

Reinhard Zumkeller, Dec 15 2012

STATUS

approved