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A251604
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A Zumkeller-type sequence (cf. A098550): a(n) = n if n <= 3, otherwise the smallest number not occurring earlier having at least one common factor with a(n-2)+a(n-1), but none with a(n-1).
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8
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1, 2, 3, 5, 4, 9, 13, 6, 19, 10, 29, 12, 41, 53, 8, 61, 15, 14, 87, 101, 16, 21, 37, 18, 11, 58, 23, 24, 47, 71, 20, 7, 27, 17, 22, 39, 122, 35, 157, 26, 33, 59, 28, 45, 73, 30, 103, 38, 51, 89, 25, 32, 57, 178, 55, 233, 34, 63, 97, 36, 49, 40, 267, 307, 42
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OFFSET
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1,2
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COMMENTS
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Conjectured to be a permutation of the positive integers.
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LINKS
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MATHEMATICA
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a[n_] := a[n] = If[n <= 3, n, For[k = 1, True, k++, If[FreeQ[Array[a, n-1], k], If[!CoprimeQ[k, a[n-2]+a[n-1]] && CoprimeQ[k, a[n-1]], Return[k]]]]];
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PROG
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(Haskell)
import Data.List (delete)
a251604 n = a251604_list !! (n-1)
a251604_list = 1 : 2 : 3 : f 2 3 [4..] where
f u v ws = g ws where
g (x:xs) = if gcd x (u + v) > 1 && gcd x v == 1
then x : f v x (delete x ws) else g xs
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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