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A039652
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Becomes prime after n iterations of f(x) = phi(x)+1 (least inverse of A039651).
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10
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2, 1, 15, 35, 69, 255, 535, 949, 1957, 2513, 2923, 4531, 17701, 22957, 54589, 79421, 80029, 84493, 98581, 102827, 115243, 239111, 291149, 310813, 362621, 398893, 598341, 801923, 838307, 1063493, 1079833, 1123813, 1311121, 1329403, 1582439
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OFFSET
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0,1
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COMMENTS
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Of the terms n <= 66, all are semiprimes except those for n = 0, 1, 5, and 19. Why? - T. D. Noe, Oct 17 2013
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LINKS
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MATHEMATICA
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nn = 34; t = Table[0, {nn}]; found = 0; n = 0; While[found < nn, n++; len = Length[NestWhileList[EulerPhi[#] + 1 &, n, UnsameQ, All]] - 2; If[len <= nn && t[[len]] == 0, t[[len]] = n; found++]]; t = Join[{2}, t] (* T. D. Noe, Oct 17 2013 *)
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CROSSREFS
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KEYWORD
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nonn,hard
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AUTHOR
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STATUS
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approved
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