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 A091859 a(1) = 2, a(n) is the least prime of the form 2k*a(n-1)+1 where 2k is the least even number not used earlier. 0
 2, 5, 31, 311, 3733, 59729, 1194581, 57339889, 1605516893, 22477236503, 1933042339259, 143045133105167, 2574812395893007, 87543621460362239, 700348971682897913, 58829313621363424693, 1411903526912722192633 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE a(2) = 5 = 2*2+1, But a(3) = 31 though 11= 5*2 +1 is also prime. PROG Contribution from Rick L. Shepherd, Sep 08 2009: (Start) (PARI) {a=[2]; terms=1; used=Set(); while(terms<30, k2=0; until(isprime(k2*a[terms]+1), until(setsearch(used, k2)==0, k2=k2+2)); a=concat(a, k2*a[terms]+1); terms++; used=setunion(used, Set([k2]))); a} (End) CROSSREFS Sequence in context: A192397 A097396 A056788 * A085873 A303289 A051048 Adjacent sequences:  A091856 A091857 A091858 * A091860 A091861 A091862 KEYWORD nonn AUTHOR Amarnath Murthy, Mar 13 2004 EXTENSIONS a(6) onwards by Rick L. Shepherd, Sep 08 2009 STATUS approved

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Last modified September 17 04:03 EDT 2019. Contains 327119 sequences. (Running on oeis4.)