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A091859
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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.
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0
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2, 5, 31, 311, 3733, 59729, 1194581, 57339889, 1605516893, 22477236503, 1933042339259, 143045133105167, 2574812395893007, 87543621460362239, 700348971682897913, 58829313621363424693, 1411903526912722192633
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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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a(2) = 5 = 2*2+1, But a(3) = 31 though 11= 5*2 +1 is also prime.
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PROG
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(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)
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CROSSREFS
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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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