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A027420 Triangle T00, T10, T01, T20, T11, T02, etc., where Tmn = number of distinct products ij with min(m,n) <= i,j <= max(m,n). 3
1, 2, 2, 4, 1, 4, 7, 3, 3, 7, 10, 6, 1, 6, 10, 15, 9, 3, 3, 9, 15, 19, 14, 6, 1, 6, 14, 19, 26, 18, 10, 3, 3, 10, 18, 26, 31, 25, 14, 6, 1, 6, 14, 25, 31, 37, 30, 20, 10, 3, 3, 10, 20, 30, 37, 43, 36, 25, 15, 6, 1, 6, 15, 25, 36, 43, 54, 42, 31, 20, 10, 3, 3, 10, 20, 31, 42, 54 (list; table; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
T(n,0) = T(n,n) = A027384(n). - Reinhard Zumkeller, May 02 2014
LINKS
MATHEMATICA
t[m_, n_] := i*j /. {ToRules @ Reduce[ Min[m, n] <= i <= j <= Max[m, n], Integers]} // Union // Length; row[n_] := Table[ t[m, n-m], {m, 0, n} ]; Table[ row[n], {n, 0, 11}] // Flatten (* Jean-François Alcover, Apr 16 2013 *)
PROG
(Haskell)
import Data.List (nub)
a027420 n k = a027420_tabl !! n !! k
a027420_row n = a027420_tabl !! n
a027420_tabl = zipWith (zipWith z) a002262_tabl a025581_tabl
where z u v = length $ nub $ [i * j | i <- zs, j <- zs]
where zs = [min u v .. max u v]
-- Reinhard Zumkeller, May 02 2014
CROSSREFS
Cf. A027384.
Cf. A241944 (row sums), A002262, A025581.
Sequence in context: A138558 A111580 A066202 * A116588 A069922 A072211
KEYWORD
tabl,nonn,easy,nice
AUTHOR
EXTENSIONS
More terms from Olivier Gérard, Nov 15 1997
STATUS
approved

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Last modified May 23 20:34 EDT 2024. Contains 372765 sequences. (Running on oeis4.)