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A225747
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a(n) = smallest prime q > a(n-1) such that 2*prime(n)*q^prime(n)+1 is also prime.
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1
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2, 3, 7, 17, 1579, 1997, 2347, 3323, 6637, 11161, 13829, 18287, 40759, 42197, 42337, 45757, 46141, 48383, 49253, 51631, 52541, 53549, 73477, 78079, 81677, 111439, 164363, 166567, 170441, 180667, 191507, 202729, 209029, 257351, 292471, 294809, 300569, 328787
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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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2*2*2^2+1=17 prime so a(1)=2,
2*3*2^3+1=49 composite,
2*3*3^3+1=163 prime so a(2)=3 as 3>2.
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MATHEMATICA
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nxt[{n_, a_}]:=Module[{p=NextPrime[a], c=Prime[n+1]}, While[!PrimeQ[ 2*c*p^c+1], p = NextPrime[ p]]; {n+1, p}]; NestList[nxt, {1, 2}, 40][[All, 2]] (* Harvey P. Dale, Jul 03 2021 *)
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PROG
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(PFGW & SCRIPTIFY)
SCRIPT
DIM n, 0
DIM k, 0
DIM q
DIMS t
OPENFILEOUT myfile, a(n).txt
LABEL a
SET n, n+1
IF n>177 THEN END
LABEL b
SET k, k+1
SET q, p(k)
SETS t, %d\,; q
PRP 2*p(n)*q^p(n)+1, t
IF ISPRP THEN GOTO c
GOTO b
LABEL c
WRITE myfile, q
GOTO a
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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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