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A074038
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If n is the k-th single (i.e., non-twin) prime then a(n) = k, otherwise a(n) = 0.
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3
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0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 8, 0, 0, 0, 0, 0, 9, 0, 0, 0, 0, 0, 0, 0, 10, 0, 0
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OFFSET
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1,23
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LINKS
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FORMULA
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MATHEMATICA
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upto = 100;
A074038list[upto_] := Module[{k = 0, v = Table[0, {upto}], n},
For[n = 1, n <= upto, n++, If[PrimeQ[n] && (2 == n ||
((!PrimeQ[n-2]) && (!PrimeQ[n+2]))), k++; v[[n]] = k,
v[[n]] = 0]]; v];
v074038 = A074038list[upto];
a[n_] := v074038[[n]];
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PROG
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(PARI)
up_to = 65537;
A074038list(up_to) = { my(k=0, v=vector(up_to)); for(n=1, up_to, if(isprime(n)&&(2==n||((!isprime(n-2))&&(!isprime(n+2)))), k++; v[n]=k, v[n] = 0)); (v); };
v074038 = A074038list(up_to);
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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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