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A136020
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Smallest prime of the form (2*n+1)*prime(k)-2*n, any k.
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58
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7, 11, 29, 19, 23, 53, 31, 103, 191, 43, 47, 101, 109, 59, 311, 67, 71, 149, 79, 83, 173, 181, 283, 197, 103, 107, 331, 229, 709, 367, 127, 131, 269, 139, 853, 293, 151, 463, 317, 163, 167, 1021, 349, 179, 547, 373, 191, 389, 199, 607, 619, 211, 643, 1091, 223
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OFFSET
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1,1
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COMMENTS
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The associated prime(k) are in A136019.
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LINKS
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EXAMPLE
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a(1)=7 because 7 is smallest prime p such that (p+2)/3 is prime
a(2)=11 because 11 is smallest prime p such that (p+4)/5 is prime
a(3)=29 because 29 is smallest prime p such that (p+6)/7 is prime
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MATHEMATICA
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a = {}; Do[k = 1; While[ !PrimeQ[(Prime[k] + 2n)/(2n + 1)], k++ ]; AppendTo[a, Prime[k]], {n, 1, 100}]; a
Reap[Do[k = PrimePi[2n+1]; While[ !PrimeQ[((p=Prime[k]) + 2n)/(2n + 1)], k++ ]; Sow[p], {n, 100}]][[2, 1]] (* Zak Seidov, Mar 04 2013 *)
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PROG
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(PARI) a(n)=my(t); n+=n; forprime(p=2, default(primelimit), if(isprime(t=(n+1)*p-n), return(t))) \\ Charles R Greathouse IV, Feb 13 2011
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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