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Search: id:A130709
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| A130709 |
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Number of compositions of n such that the largest part is coprime to every other part. |
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+0
1
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| 1, 1, 2, 4, 7, 13, 22, 41, 75, 138, 255, 482, 911, 1735, 3316, 6370, 12306, 23907, 46666, 91500, 180119, 355820, 705061, 1400722, 2788718, 5561720, 11107305, 22205839, 44429088, 88942741, 178120533, 356787834, 714732794, 1431763102, 2867860060
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OFFSET
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0,3
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FORMULA
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G.f.: 1/(1-x) + Sum_{n>1} x^n/(1-Sum_{d | 1<=d<=n, gcd(n,d)=1} x^d)^2.
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MAPLE
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A130709 := proc(n) local gf, den, i, d ; gf := 0 ; for i from 2 to n do den := 1 ; for d from 1 to i-1 do if gcd(d, i) = 1 then den := den-x^d ; fi ; od ; gf := taylor(gf+x^i/den^2, x=0, n+1) ; od: 1+coeftayl(gf, x=0, n) ; end: seq(A130709(n), n=0..40) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 28 2007
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CROSSREFS
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Sequence in context: A128768 A001036 A054150 this_sequence A073832 A051013 A128609
Adjacent sequences: A130706 A130707 A130708 this_sequence A130710 A130711 A130712
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KEYWORD
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easy,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)Eunet.yu), Jul 01 2007
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 28 2007
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