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A098170
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Smallest prime p such that prime(n)#/2 + 2*p is prime where p > 3, except p=2 for n=1.
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2
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2, 5, 7, 11, 13, 19, 29, 31, 29, 31, 41, 41, 43, 83, 59, 83, 163, 97, 193, 89, 89, 173, 113, 107, 131, 157, 131, 109, 113, 467, 151, 239, 167, 263, 233, 211, 251, 167, 599, 199, 199, 211, 313, 241, 509, 887, 307, 227, 419, 479, 317, 269, 653, 281, 307, 277, 499
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OFFSET
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1,1
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LINKS
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EXAMPLE
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For n=4, A002110(4)/2=210/2=105. 105+2*5 is not prime. 105+2*7 is not prime. 105+2*11 is prime, so a(4)=11.
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MAPLE
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local pri, j, jmin;
if n = 1 then
jmin := 1;
else
jmin := 3;
end if;
for j from jmin do
if isprime(pri+2*ithprime(j)) then
return ithprime(j) ;
end if;
end do:
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MATHEMATICA
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Primorial[n_Integer] := Block[{k = Product[ Prime[ j], {j, n}]}, k]; f[n_] := Block[{p = Primorial[n]/2}, If[n == 1, j = 1, j = 2]; While[ !PrimeQ[p + 2Prime[j]], j++ ]; Prime[j]]; Table[ f[n], {n, 57}] (* Robert G. Wilson v, Sep 04 2004 *)
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CROSSREFS
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The indices of the p are in A098171.
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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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