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A130709 Number of compositions of n such that the largest part is coprime to every other part. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..34.

FORMULA

G.f.: 1/(1-x) + Sum_{n>1} x^n/(1-Sum_{d | 1<=d<=n, gcd(n,d)=1} x^d)^2.

MAPLE

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, Oct 28 2007

CROSSREFS

Sequence in context: A254007 A001036 A054150 * A051013 A128609 A168043

Adjacent sequences:  A130706 A130707 A130708 * A130710 A130711 A130712

KEYWORD

easy,nonn

AUTHOR

Vladeta Jovovic, Jul 01 2007

EXTENSIONS

More terms from R. J. Mathar, Oct 28 2007

STATUS

approved

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Last modified December 10 21:53 EST 2019. Contains 329909 sequences. (Running on oeis4.)