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 A057606 Triangle read by rows: T(n,k) = number of binary n-tuples u having exactly k grandchildren, where a grandchild is a vector obtained by deleting any two coordinates of u (n >= 3, 1<=k<=2^(n-2)). 2
 2, 6, 2, 4, 6, 4, 2, 4, 8, 4, 8, 4, 2, 0, 2, 4, 10, 6, 12, 8, 8, 6, 6, 0, 2, 0, 0, 0, 0, 0, 2, 4, 12, 8, 16, 14, 16, 12, 12, 12, 6, 4, 8, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 4, 14, 10, 20, 22, 24, 22, 22, 26, 18, 16, 12, 16, 12, 0, 4, 10, 0, 0, 0, 2, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,1 COMMENTS Row lengths = 2^(n-2), row sums = 2^n. REFERENCES N. J. A. Sloane, On single-deletion-correcting codes, in Codes and Designs (Columbus, OH, 2000), 273-291, Ohio State Univ. Math. Res. Inst. Publ., 10, de Gruyter, Berlin, 2002. LINKS Reinhard Zumkeller, Rows n = 3..15 of triangle, flattened N. J. A. Sloane, On single-deletion-correcting codes EXAMPLE 2,6; 2,4,6,4; 2,4,8,4,8,4,2,0; ... PROG (Haskell) import Data.List (group, sort, nub, inits, tails) a057606 n k = a057606_tabf !! (n-3) !! (k-1) a057606_row n = a057606_tabf !! (n-3) a057606_tabf = map g \$ drop 3 \$ iterate (\xs -> (map (0 :) xs) ++ (map (1 :) xs)) [[]] where g xss = map length \$ fill0 \$ group \$ sort \$ map (length . del2) xss where fill0 uss = f0 uss [1 .. length xss `div` 4] where f0 _ [] = [] f0 [] (j:js) = [] : f0 [] js f0 vss'@(vs:vss) (j:js) | j == head vs = vs : f0 vss js | otherwise = [] : f0 vss' js del2 = nub . (concatMap del1) . del1 del1 xs = nub \$ zipWith (++) (init \$ inits xs) (map tail \$ init \$ tails xs) -- Reinhard Zumkeller, Apr 30 2012 CROSSREFS Cf. A057607. Sequence in context: A151944 A073094 A194953 * A021385 A085193 A220242 Adjacent sequences: A057603 A057604 A057605 * A057607 A057608 A057609 KEYWORD nonn,tabf,nice AUTHOR N. J. A. Sloane, Oct 08 2000 STATUS approved

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Last modified February 22 09:09 EST 2024. Contains 370250 sequences. (Running on oeis4.)