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A224609
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Smallest j such that 2*j*prime(n)^3-1 is prime.
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5
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2, 1, 2, 7, 2, 7, 8, 6, 8, 5, 1, 3, 11, 1, 9, 3, 5, 1, 3, 15, 7, 3, 8, 8, 12, 2, 15, 3, 10, 2, 3, 12, 12, 1, 6, 6, 9, 3, 5, 2, 5, 1, 5, 10, 57, 1, 21, 1, 15, 9, 2, 3, 1, 5, 5, 3, 15, 6, 7, 5, 25, 6, 12, 11, 6, 5, 1, 9, 2, 19, 5, 9, 27, 1, 3, 11, 3, 15, 2, 6, 21
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OFFSET
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1,1
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COMMENTS
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We are searching smallest j such that j*prime(n)*2*p(n)^2-1 is prime, for A224489 it is smallest k such that k*2*prime(n)^2-1 is prime, so here we replace smallest k by smallest j*prime(n).
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LINKS
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FORMULA
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EXAMPLE
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1*2*2^3-1= 15 is composite; 2*2*2^3-1= 31 is prime, so a(1)=2 as p(1)=2.
1*2*3^3-1=53 is prime, so a(2)=1 as p(2)=3.
1*2*5^3-1=249 is composite; 2*2*5^3=499 is prime, so a(3)=2 as p(3)=5.
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MATHEMATICA
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jmax = 10^5 (* sufficient up to 10^5 terms *); a[n_] := For[j = 1, j <= jmax, j++, p = Prime[n]; If[PrimeQ[j*2*p^3 - 1], Return[j]]]; Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Apr 18 2013 *)
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PROG
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(Magma)
S:=[];
j:=1;
for n in [1..100] do
while not IsPrime(2*j*NthPrime(n)^3-1) do
j:=j+1;
end while;
Append(~S, j);
j:=1;
end for;
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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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