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A276052
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Least k > 1 such that phi(k*n-1) = phi(k*n+1), or -1 if no such k exists.
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1
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5, 4, 3, 2, 15, 106, 21, 127, 3, 39282, 3, 53, 135, 65014, 5, 9489, 171, 361, 27, 19641, 7, 13133, 141, 6326, 3, 6978, 19, 32507, 375, 13094, 165, 93186, 19, 1359, 9, 12588, 15, 171, 45, 35253, 3, 35794, 9, 16796, 7, 1689, 69, 3163, 3, 13653, 57, 3489, 12, 249, 45, 58497, 9
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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a(5) = 15 because phi(15*5-1) = phi(15*5+1).
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MAPLE
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f:= proc(n) local k;
for k from 2 do if numtheory:-phi(k*n-1) = numtheory:-phi(k*n+1) then
return k
fi od end proc:
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MATHEMATICA
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kmax = 10^9;
a[n_] := Module[{k}, For[k = 2, k <= kmax, k++, If[EulerPhi[k n - 1] == EulerPhi[k n + 1] , Print[n, " ", k]; Return[k]]]; -1];
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PROG
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(PARI) a(n) = {my(k = 2); while (eulerphi(k*n+1) != eulerphi(k*n-1), k++); k; }
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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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