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A143482
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a(1)=1. For n>1, a(n) = the smallest positive multiple of n such that phi(a(n)) >= phi(a(n-1)), where phi(m) is A000010(m).
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6
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1, 2, 3, 4, 5, 12, 7, 16, 27, 50, 33, 72, 39, 56, 45, 64, 51, 108, 57, 100, 105, 154, 115, 288, 125, 286, 243, 392, 203, 690, 217, 416, 363, 544, 455, 864, 407, 836, 663, 1000, 451, 1512, 559, 1276, 1125, 1334, 799, 2256, 931, 2000, 1377, 1924, 1007, 2862, 1375
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OFFSET
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1,2
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COMMENTS
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A143480 is an analogous sequence but with phi(a(n)) > phi(a(n-1)).
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LINKS
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EXAMPLE
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a(9) = 27 because:
phi(9) = 6 < 8 = phi(a(8)),
phi(18) = 6 < 8 = phi(a(8)),
phi(27) = 18 >= 8 = phi(a(8)).
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MATHEMATICA
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a = t = {1}; lim = 55; Do[k = 1; While[EulerPhi[k n] < t[[n - 1]], k++]; AppendTo[a, k n]; AppendTo[t, EulerPhi[k n]], {n, 2, lim}]; a (* Michael De Vlieger, Sep 04 2015 *)
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PROG
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(PARI) lista(nn) = {print1(a=1, ", "); for (n=2, nn, k = 1; phia = eulerphi(a); while(eulerphi(k*n) < phia, k++); a = k*n; print1(a, ", "); ); } \\ Michel Marcus, Sep 22 2015
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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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