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A183218 Complement of the hexagonal numbers. 3
2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(n)=n+Floor[1/2+(n/2)^(1/2)].

EXAMPLE

Hexagonal numbers: (1,6,15,28,45,...) = A000384,

so that A183218=(2,3,4,5,7,8,9,...,14,16,...,27,29,...).

MATHEMATICA

Table[n+Floor[1/2+(n/2)^(1/2)], {n, 100}]

Module[{nn=110}, Complement[Range[nn], PolygonalNumber[6, Range[ Floor[ (1+Sqrt[ 1+8nn])/4]]]]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 22 2020 *)

CROSSREFS

Cf. A000384.

Sequence in context: A052414 A095410 A022293 * A071000 A088451 A047595

Adjacent sequences:  A183215 A183216 A183217 * A183219 A183220 A183221

KEYWORD

nonn

AUTHOR

Clark Kimberling, Jan 01 2011

STATUS

approved

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Last modified May 8 07:02 EDT 2021. Contains 343653 sequences. (Running on oeis4.)