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A066200
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a(1) = 1; for n > 1, a(n) = a(n-1)-(n+2) if this is positive and has not already appeared, otherwise a(n) = a(n-1)+(n+2).
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2
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1, 5, 10, 4, 11, 3, 12, 2, 13, 25, 38, 24, 9, 25, 8, 26, 7, 27, 6, 28, 51, 75, 50, 76, 49, 21, 50, 20, 51, 19, 52, 18, 53, 17, 54, 16, 55, 15, 56, 14, 57, 101, 146, 100, 147, 99, 148, 98, 47, 99, 46, 100, 45, 101, 44, 102, 43, 103, 42, 104, 41, 105, 40, 106, 39, 107, 176
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listen;
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OFFSET
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1,2
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LINKS
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MAPLE
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S:= {1}:
a[1]:= 1:
for n from 2 to 100 do
t:=a[n-1]-(n+2);
if t > 0 and not member(t, S) then
a[n]:= t
else
a[n]:= a[n-1]+(n+2)
fi;
S:= S union {a[n]}
od:
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PROG
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(Python)
l=[0, 1]
for n in range(2, 101):
x=l[n - 1] - (n + 2)
if x>0 and x not in l: l.append(x)
else: l.append(l[n - 1] + (n + 2))
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CROSSREFS
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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