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A080579
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a(1)=1; for n>1, a(n)=a(n-1)+1 if n is already in the sequence, a(n)=a(n-1)+4 otherwise.
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1
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1, 5, 9, 13, 14, 18, 22, 26, 27, 31, 35, 39, 40, 41, 45, 49, 53, 54, 58, 62, 66, 67, 71, 75, 79, 80, 81, 85, 89, 93, 94, 98, 102, 106, 107, 111, 115, 119, 120, 121, 122, 126, 130, 134, 135, 139, 143, 147, 148, 152, 156, 160, 161, 162, 166, 170, 174, 175
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OFFSET
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1,2
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LINKS
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MATHEMATICA
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a[1] = 1; a[n_] := a[n] = If[MemberQ[Array[a, n-1], n], a[n-1]+1, a[n-1]+4]; Array[a, 60] (* Jean-François Alcover, Oct 08 2018 *)
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PROG
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(Haskell)
a080579 n = a080579_list !! (n-1)
a080579_list = 1 : f 2 [1] where
f x zs@(z:_) = y : f (x + 1) (y : zs) where
y = if x `elem` zs then z + 1 else z + 4
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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