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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-Fran├žois 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.)