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 A045975 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,... 6
 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 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A generalized Connell sequence. LINKS Reinhard Zumkeller, Rows n=1..150 of triangle, flattened EXAMPLE 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, ... MATHEMATICA 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 *) PROG (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 -- Reinhard Zumkeller, Jan 18 2012 CROSSREFS Cf. A001614, A033291. Seen as a triangle read by rows: cf. A204558 (row sums), A005917 (central terms), A204556 (left edge), A204557 (right edge). Sequence in context: A036277 A042960 A266596 * A058296 A025217 A119759 Adjacent sequences:  A045972 A045973 A045974 * A045976 A045977 A045978 KEYWORD nonn,easy,nice,tabl AUTHOR Fang-kuo Huang (gsyps(AT)ms17.hinet.net) EXTENSIONS More terms from James A. Sellers Keyword tabl added by Reinhard Zumkeller, Jan 18 2012 STATUS approved

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Last modified October 23 14:06 EDT 2018. Contains 316528 sequences. (Running on oeis4.)