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A080574
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a(1)=1, a(n)=a(n-1)+1 if n is odd and already in the sequence, a(n)=a(n-1)+2 if n is even and already in the sequence, a(n)=a(n-1)+3 otherwise.
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1
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1, 4, 7, 9, 12, 15, 16, 19, 20, 23, 26, 28, 31, 34, 35, 37, 40, 43, 44, 46, 49, 52, 53, 56, 59, 61, 64, 66, 69, 72, 73, 76, 79, 81, 82, 85, 86, 89, 92, 94, 97, 100, 101, 103, 106, 108, 111, 114, 115, 118, 121, 123, 124, 127, 130, 132, 135, 138, 139, 142
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OFFSET
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1,2
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LINKS
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FORMULA
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It appears that a(n) is asymptotic to c*n where c=2.36... is the largest root of q^2-3*q+3/2 = 0.
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MATHEMATICA
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a[1] = 1;
a[n_] := a[n] = If[MemberQ[Array[a, n-1], n], If[OddQ[n], a[n-1]+1, a[n-1]+2], a[n-1]+3];
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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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