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A137519
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a(1)=1. a(2)=2. For n>=3, a(n) = the smallest integer > a(n-1) that is coprime to (a(n-1)+1)*(a(n-2)+1).
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1
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1, 2, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 39, 41, 43, 47, 49, 53, 59, 61, 67, 69, 71, 73, 77, 79, 83, 89, 97, 101, 103, 107, 109, 113, 119, 121, 127, 129, 131, 133, 137, 139, 143, 149, 151, 157, 159, 161, 163, 167, 169, 173, 179, 181, 187, 191, 193, 197, 199, 203
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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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N:= 100: # for a(1)..a(N)
A[1]:= 1: A[2]:= 2:
for n from 3 to N do
t:= (A[n-1]+1)*(A[n-2]+1);
for k from A[n-1]+1 do
if igcd(k, t)=1 then
A[n]:= k;
break
fi
od;
od:
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MATHEMATICA
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a = {1, 2}; For[n = 3, n < 80, n++, i = a[[ -1]] + 1; While[GCD[(a[[ -1]] + 1)*(a[[ -2]] + 1), i] > 1, i++ ]; AppendTo[a, i]]; a (* Stefan Steinerberger, Apr 26 2008 *)
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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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