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A192521 Monotonic ordering of set S generated by these rules:  if x and y are in S then floor((x+1)(y+1)/2) is in S, and 2 is in S. 2
2, 4, 7, 12, 19, 20, 30, 31, 32, 46, 48, 49, 50, 52, 70, 73, 75, 76, 77, 79, 80, 82, 84, 106, 111, 114, 115, 117, 120, 121, 122, 124, 125, 127, 128, 130, 132, 136, 160, 168, 172, 174, 177, 181, 183, 184, 185, 187, 188, 189, 190, 192, 193, 195, 196, 199, 200 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..57.

MATHEMATICA

start = {2}; f[x_, y_] := Floor[(x + 1)*(y + 1)/2]

b[x_] :=

  Block[{w = x},

   Select[Union[

     Flatten[AppendTo[w,

       Table[f[w[[i]], w[[j]]], {i, 1, Length[w]}, {j, 1, i}]]]], # <

      400 &]];

t = NestList[b, start, 14][[-1]] (* A192521 *)

Table[t[[i]] - t[[i - 1]], {i, 2, Length[t]}]  (* differences *)

CROSSREFS

Cf. A192476.

Sequence in context: A230118 A105807 A209616 * A066699 A188425 A087149

Adjacent sequences:  A192518 A192519 A192520 * A192522 A192523 A192524

KEYWORD

nonn

AUTHOR

Clark Kimberling, Jul 03 2011

STATUS

approved

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Last modified September 28 01:27 EDT 2021. Contains 347698 sequences. (Running on oeis4.)