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A127689
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a(1)=3; for n>1, a(n) is least number such that a(1)^2+...+a(n)^2 is a square.
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1
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3, 4, 12, 84, 132, 12324, 15960, 26280, 27300, 66660, 115188
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| a(2)=4 because 3^2+4^2=5^2, a(3)=12 because 3^2+4^2+12^2=13^2 etc.
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MATHEMATICA
| a = {3}; For[k = 1 + a[[Length[a]]], Length[a] < 11, While[ ! IntegerQ[Sqrt[(k)^2 + Sum[(a[[t]])^2, {t, 1, Length[a]}]]], k++ ]; AppendTo[a, k]]; a
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CROSSREFS
| Cf. A018930, A127690, A127691.
Sequence in context: A122903 A059792 A018930 * A127690 A092417 A071543
Adjacent sequences: A127686 A127687 A127688 * A127690 A127691 A127692
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KEYWORD
| nonn
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AUTHOR
| Artur Jasinski (grafix(AT)csl.pl), Jan 23 2007
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