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A029907
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a(n+1) = a(n) + a(n-1) + Fibonacci(n), with a(0) = 0 and a(1) = 1.
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31
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0, 1, 2, 4, 8, 15, 28, 51, 92, 164, 290, 509, 888, 1541, 2662, 4580, 7852, 13419, 22868, 38871, 65920, 111556, 188422, 317689, 534768, 898825, 1508618, 2528836, 4233872, 7080519, 11828620, 19741179, 32916068, 54835556, 91276202, 151814645, 252318312
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OFFSET
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0,3
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COMMENTS
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Number of matchings of the fan graph on n vertices, n>0 (a fan is the join of the path graph with one extra vertex).
Number of parts in all compositions of n into odd parts. Example: a(5)=15 because the compositions 5, 311, 131, 113, and 11111 have a total of 1+3+3+3+5=15 parts.
a(n-1) is the number of compositions of n that contain one even part; for example, a(5-1)=a(4)=8 counts the compositions 1112, 1121, 1211, 14, 2111, 23, 32, 41. - Joerg Arndt, May 21 2013
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LINKS
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FORMULA
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G.f.: x*(1-x^2)/(1-x-x^2)^2.
a(n) = ((n+4)*Fibonacci(n) + 2*n*Fibonacci(n-1))/5.
a(n+1) = Sum_{k=0..n} Sum_{j=0..floor(k/2)} binomial(n-j, j). - Paul Barry, Oct 23 2004
a(n) = F(n) + Sum_{k=1..n-1} F(k)*F(n-k), where F=Fibonacci. - Reinhard Zumkeller, Nov 01 2013
E.g.f.: exp(x/2)*(5*x*cosh(sqrt(5)*x/2) + sqrt(5)*(5*x + 8)*sinh(sqrt(5)*x/2))/25. - Stefano Spezia, Dec 04 2023
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EXAMPLE
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a(4)=8 because matchings of fan graph with edges {OA,OB,OC,AB,AC} are: {},{OA},{OB},{OC},{AB},{AC},{OA,BC},{OC,AB}.
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MAPLE
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with(combinat); A029907 := proc(n) options remember; if n <= 1 then n else procname(n-1)+procname(n-2)+fibonacci(n-1); fi; end;
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MATHEMATICA
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CoefficientList[Series[x(1-x^2)/(1-x-x^2)^2, {x, 0, 37}], x] (* or *)
a[n_]:= a[n]= a[n-1] +a[n-2] +Fibonacci[n-1]; a[0]=0; a[1]=1; Array[a, 37] (* or *)
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PROG
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(PARI) alias(F, fibonacci); a(n)=((n+4)*F(n)+2*n*F(n-1))/5;
(Haskell)
a029907 n = a029907_list !! n
a029907_list = 0 : 1 : zipWith (+) (tail a000045_list)
(zipWith (+) (tail a029907_list) a029907_list)
(Magma) [((n+4)*Fibonacci(n)+2*n*Fibonacci(n-1))/5: n in [0..40]]; // Vincenzo Librandi, Feb 25 2018
(SageMath)
def A029907(n): return (1/5)*(n*lucas_number2(n, 1, -1) + 4*fibonacci(n))
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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