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A130109 Rearrangement of natural numbers such that each two terms sum up to a perfect square. 3
1, 3, 2, 7, 4, 5, 6, 10, 8, 17, 9, 16, 11, 14, 12, 13, 15, 21, 18, 31, 19, 30, 20, 29, 22, 27, 23, 26, 24, 25, 28, 36, 32, 49, 33, 48, 34, 47, 35, 46, 37, 44, 38, 43, 39, 42, 40, 41, 45, 55, 50, 71, 51, 70, 52, 69, 53, 68, 54, 67, 56, 65, 57, 64, 58, 63, 59, 62, 60, 61, 66, 78 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..72.

EXAMPLE

1+3=4, 2+7=9, 4+5=9, 6+10=16, 8+17=25.

MATHEMATICA

s={}; ra=Range[2000]; Do[su=ra[[1]]; c=2; While[ !IntegerQ[Sqrt[su+ra[[c]]]], c++ ]; rac=ra[[c]]; s=Join[s, {ra[[1]], rac}]; ra=Complement[ra, {ra[[1]], rac}], {133}]; s

CROSSREFS

Cf. A130108, A130110, A130111.

Sequence in context: A129187 A166532 A135542 * A153151 A175057 A153154

Adjacent sequences:  A130106 A130107 A130108 * A130110 A130111 A130112

KEYWORD

nonn

AUTHOR

Zak Seidov, May 08 2007

STATUS

approved

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Last modified March 22 04:32 EDT 2019. Contains 321406 sequences. (Running on oeis4.)