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Composite Fibonacci sequence: each term is the composite with index equal to the sum of the previous two terms.
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%I #7 Nov 18 2018 01:09:06

%S 4,6,18,36,76,147,285,532,984,1795,3237,5793,10293,18168,31887,55709,

%T 96926,167972,290136,499615,857947,1469576,2511369,4282663,7289002,

%U 12383250,21002336,35564859,60136917,101547211,171253466,288461204

%N Composite Fibonacci sequence: each term is the composite with index equal to the sum of the previous two terms.

%C What is the value of lim_{n -> infinity} a(n)/a(n+1)? - _Ryan Propper_, Jan 11 2007

%F a(n) = A002808(a(n-1) + a(n-2)); a(1)=4, a(2)=6.

%e a(5) = A002808(18 + 36) = A002808(54) = 76.

%t Composite[n_Integer] := FixedPoint[n + PrimePi[ # ] + 1 &, n + PrimePi[n] + 1]; a = 4; b = 6; Do[c = Composite[a + b]; Print[c]; a = b; b = c, {n, 100}] (* _Ryan Propper_, Jan 11 2007 *)

%Y Cf. A002808, A000045, A107327.

%K nonn,easy

%O 1,1

%A Christopher M. Tomaszewski (cmt1288(AT)comcast.net), May 24 2005

%E More terms from _Ryan Propper_, Jan 11 2007