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A072209
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Number of primitive roots of those integers with at least one primitive root.
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2
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1, 1, 1, 1, 2, 1, 2, 2, 2, 4, 4, 2, 8, 2, 6, 4, 10, 8, 4, 6, 12, 8, 8, 12, 6, 16, 12, 10, 22, 12, 8, 24, 6, 12, 28, 16, 8, 20, 24, 24, 12, 24, 18, 16, 40, 12, 40, 22, 32, 12, 40, 32, 24, 52, 36, 48, 28, 40, 16, 40, 36, 48, 20, 64, 44, 24, 24, 72, 40, 48, 24, 18, 54
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OFFSET
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1,5
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COMMENTS
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Essentially sequence A046144 with all zero entries deleted.
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LINKS
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FORMULA
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MATHEMATICA
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Reap[ Do[ If[n == 1, Sow[1], If[ IntegerQ[ PrimitiveRoot[n]], Sow[ EulerPhi[ EulerPhi[n]]]]] , {n, 1, 100}]][[2, 1]] (* Jean-François Alcover, Feb 24 2012 *)
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PROG
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(PARI) is(n)=if(n%2, isprimepower(n) || n==1, n==2 || n==4 || (isprimepower(n/2, &n) && n>2));
lista(nn) = for (n=1, nn, if (is(n), print1(eulerphi(eulerphi(n)), ", "))); \\ Michel Marcus, May 12 2017
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CROSSREFS
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KEYWORD
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nice,nonn
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AUTHOR
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STATUS
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approved
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