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A087274
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Prime index of the largest prime factor of 3*prime(n)+1.
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3
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4, 3, 1, 5, 7, 3, 6, 10, 4, 5, 15, 4, 11, 6, 20, 3, 24, 9, 26, 28, 5, 7, 3, 19, 21, 8, 11, 9, 13, 7, 43, 45, 27, 8, 4, 49, 17, 4, 54, 6, 57, 7, 13, 10, 12, 9, 66, 19, 11, 14, 4, 72, 42, 10, 44, 22, 26, 12, 6, 47, 7, 5, 89, 91, 15, 7, 20, 9, 98, 32, 16, 5, 10, 4, 104, 9, 21, 35, 14, 63, 12, 22
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OFFSET
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1,1
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LINKS
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FORMULA
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EXAMPLE
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n=10: prime(10)=29, max-p-factor(88)=11, pi(11)=5=a(10)<n;
n=11: prime(11)=31, max-p-factor(94)=47, pi(47)=15=a(11)>n;
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MATHEMATICA
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ffi[x_] := Flatten[FactorInteger[x]]; ma[x_] := Part[Reverse[ffi[x]], 2]; Table[PrimePi[ma[3*Prime[w]+1]], {w, 1, 100}]
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PROG
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(PARI) a(n) = primepi(vecmax(factor(3*prime(n)+1)[, 1])); \\ Michel Marcus, Mar 27 2020
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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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