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A212147 (A212146(n)-1)/2. 3
0, 1, 3, 6, 11, 18, 29, 45, 70, 108, 170, 270, 439, 726, 1227, 2108, 3685, 6523, 11687, 21129, 38513, 70649, 130347, 241610, 449735, 840134, 1574537, 2959350, 5576730, 10533846, 19940812, 37823859, 71878024, 136827410, 260884686, 498167480, 952607343 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

A212146(n) is the number of subsets of {1,...,n} having mean=median.

LINKS

Hiroaki Yamanouchi, Table of n, a(n) for n = 1..100

MATHEMATICA

t[n_, k_] := t[n, k] = Count[Map[Median[#] == Mean[#] &, Subsets[Range[n], {k}]], True]

Flatten[Table[t[n, k], {n, 1, 12}, {k, 1, n}]]  (* A212139 *)

TableForm[Table[t[n, k], {n, 1, 12}, {k, 1, n}]]

s[n_] := Sum[t[n, k], {k, 1, n}]

Table[s[n], {n, 1, 22}]   (* A212146 *)

(% - 1)/2                 (* A212147 *)

(* Peter J. C. Moses, May 01 2012 *)

Cf. A212138.

CROSSREFS

Sequence in context: A281689 A026905 A286272 * A066778 A265075 A147079

Adjacent sequences:  A212144 A212145 A212146 * A212148 A212149 A212150

KEYWORD

nonn

AUTHOR

Clark Kimberling, May 06 2012

EXTENSIONS

a(23)-a(37) from Hiroaki Yamanouchi, Oct 03 2014

STATUS

approved

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Last modified October 17 10:43 EDT 2017. Contains 293469 sequences.