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 A074662 a(n) = F(n+1)+cos(n*Pi/2). 2
 2, 1, 1, 3, 6, 8, 12, 21, 35, 55, 88, 144, 234, 377, 609, 987, 1598, 2584, 4180, 6765, 10947, 17711, 28656, 46368, 75026, 121393, 196417, 317811, 514230, 832040, 1346268, 2178309, 3524579, 5702887, 9227464, 14930352, 24157818, 39088169 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) is the convolution of L(n) with the sequence (1,0,-1,0,1,0,-1,0,....) A056594. a(2n+1)=F(2n+2), F = Fibonacci numbers. a(n)=Sum((-1)^(i+Floor(n/2))L(2i+e),(i=0,..,Floor(n/2))), where L(n) Lucas numbers and e=(1/2)(1-(-1)^n). LINKS Index entries for linear recurrences with constant coefficients, signature (1,0,1,1) FORMULA a(n)=a(n-1)+a(n-3)+a(n-4), a(0)=2, a(1)=1, a(2)=1, a(3)=3. G.f.: (2 - x)/(1 - x - x^3 - x^4). a(4n)=F(4n+1)+1, a(4n+2)=F(4n+3)-1. a(n+1)*a(n+3) = a(n)*a(n+2) + a(n+1)*a(n+2) for all n in Z. - Michael Somos, Jan 19 2014 EXAMPLE G.f. = 2 + x + x^2 + 3*x^3 + 6*x^4 + 8*x^5 + 12*x^6 + 21*x^7 + 35*x^8 + ... MATHEMATICA CoefficientList[Series[(2 - x)/(1 - x - x^3 - x^4), {x, 0, 40}], x] a[ n_] := Fibonacci[n + 1] + Re[I^n] (* Michael Somos, Jan 19 2014 *) PROG (PARI) {a(n) = fibonacci(n+1) + real(I^n)} /* Michael Somos, Jan 19 2014 */ CROSSREFS Cf. A000045, A056594. Sequence in context: A320574 A060517 A163181 * A025243 A341014 A145085 Adjacent sequences:  A074659 A074660 A074661 * A074663 A074664 A074665 KEYWORD easy,nonn AUTHOR Mario Catalani (mario.catalani(AT)unito.it), Aug 29 2002 STATUS approved

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Last modified December 8 17:01 EST 2021. Contains 349596 sequences. (Running on oeis4.)