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A045975
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Take the first odd integer and multiple of 1, the next 2 even integers and multiples of 2, the next 3 odd integers and multiples of 3, the next 4 even integers and multiples of 4, ...
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6
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1, 2, 4, 9, 15, 21, 24, 28, 32, 36, 45, 55, 65, 75, 85, 90, 96, 102, 108, 114, 120, 133, 147, 161, 175, 189, 203, 217, 224, 232, 240, 248, 256, 264, 272, 280, 297, 315, 333, 351, 369, 387, 405, 423, 441, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 561, 583, 605, 627, 649, 671, 693
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OFFSET
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1,2
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COMMENTS
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A generalized Connell sequence.
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LINKS
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EXAMPLE
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Triangle begins:
1;
2, 4;
9, 15, 21;
24, 28, 32, 36;
45, 55, 65, 75, 85;
90, 96, 102, 108, 114, 120;
133, 147, 161, 175, 189, 203, 217;
...
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MATHEMATICA
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first[n_?EvenQ] := (n - 1)*n^2/2; first[n_?OddQ] := n*(n^2 - 2n + 3)/2; row[n_] := (ro = {first[n]}; next = first[n] + n; While[ Length[ro] < n, If[Mod[next , 2] == Mod[n, 2], AppendTo[ro, next]]; next = next + n]; ro); Flatten[ Table[row[n], {n, 1, 11}]](* Jean-François Alcover, Jun 08 2012 *)
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PROG
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(Haskell)
a045975 n k = a045975_tabl !! (n-1) !! (k-1)
a045975_row n = a045975_tabl !! (n-1)
a045975_tabl = f 1 [1..] where
f k xs = ys : f (k+1) (dropWhile (<= last ys) xs) where
ys | even k = take k ms
| otherwise = take k $ filter odd ms
ms = filter ((== 0) . (`mod` k)) xs
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CROSSREFS
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KEYWORD
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AUTHOR
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Fang-kuo Huang (gsyps(AT)ms17.hinet.net)
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EXTENSIONS
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STATUS
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approved
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