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A033291
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A Connell-like sequence: take the first multiple of 1, the next 2 multiples of 2, the next 3 multiples of 3, etc.
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6
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1, 2, 4, 6, 9, 12, 16, 20, 24, 28, 30, 35, 40, 45, 50, 54, 60, 66, 72, 78, 84, 91, 98, 105, 112, 119, 126, 133, 136, 144, 152, 160, 168, 176, 184, 192, 198, 207, 216, 225, 234, 243, 252, 261, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 374, 385, 396, 407, 418, 429, 440, 451, 462
(list; table; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| Reinhard Zumkeller, Rows n = 1..100, flattened
Gary E. Stevens, A Connell-Like Sequence, J. Integer Sequences, 1 (1998), #98.1.4.
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FORMULA
| a(n) = q(n)*n-q(n)*floor(q(n)*(q(n)+1)/6) with q(n) = ceil((1/2)*(-1+sqrt(1+8*(n)))).
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EXAMPLE
| Triangle begins
1;
2, 4;
6, 9, 12;
16, 20, 24, 28;
30, 35, 40, 45, 50;
54, 60, 66, 72, 78, 84;
91, 98, 105, 112, 119, 126, 133; ...
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MATHEMATICA
| Flatten[ Table[ n*(Floor[ (n-1)^2/3] + k), {n, 1, 12}, {k, 1, n}]] (* From Jean-François Alcover, Sep 30 2011 *)
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PROG
| (Haskell)
a033291 n k = a033291_tabl !! (n-1) !! (k-1)
a033291_row n = a033291_tabl !! (n-1)
a033291_tabl = f 1 [1..] where
f k xs = ys : f (k+1) (dropWhile (<= last ys) xs) where
ys = take k $ filter ((== 0) . (`mod` k)) xs
a192735 n = head $ a033291_tabl !! (n-1)
a192736 n = last $ a033291_tabl !! (n-1)
-- Reinhard Zumkeller, Jan 18 2012, Jul 08 2011
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CROSSREFS
| Cf. A192735 (left edge), A192736 (right edge).
Cf. A045975, A033292, A033293.
Sequence in context: A053096 A155752 A145801 * A105434 A145196 A061536
Adjacent sequences: A033288 A033289 A033290 * A033292 A033293 A033294
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KEYWORD
| nonn,easy,nice,tabl
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AUTHOR
| Gary E. Stevens (StevensG(AT)Hartwick.edu)
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EXTENSIONS
| More terms from David Radcliffe (dradcliffe(AT)gmail.com)
Corrected and formula added by Johannes W. Meijer (meijgia(AT)hotmail.com), Oct 07 2010
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