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1, 1, 2, 2, 3, 2, 3, 3, 3, 3, 4, 2, 3, 3, 3, 3, 4, 3, 4, 3, 3, 4, 5, 3, 4, 3, 4, 3, 4, 3, 4, 4, 4, 4, 3, 3, 4, 4, 3, 3, 4, 3, 4, 4, 3, 5, 6, 3, 4, 4, 4, 3, 4, 4, 4, 3, 4, 4, 5, 3, 4, 4, 3, 4, 3, 4, 5, 4, 5, 3, 4, 3, 4, 4, 4, 4, 4, 3, 4, 3, 5, 4, 5, 3, 4, 4, 4, 4, 5, 3
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OFFSET
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1,3
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COMMENTS
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For any fixed integer n > 0, the sequence 2 mod n, 2^2 mod n, 2^2^2 mod n, that is, the sequence {A014221(i) mod n} for i >= 1 is eventually constant. a(n) is the least index k such that A014221(k) mod n equals this constant.
A038081(k+1) is the largest n such that a(n) = k.
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LINKS
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FORMULA
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If A014221(k) == b(k) mod eulerphi(n), 0 < b(k) <= eulerphi(n), then a(n) is the least m > 0 such that 2^b(m-1) == 2^b(m) mod n.
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EXAMPLE
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2, 4, 16, ... mod 6 equal 2, 4, 4, ..., so A014221(k) mod 6 = 4 for all k >= 2, hence a(6) = 2.
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PROG
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(PARI) a(n) = {c=0; k=1; x=1; d=n; while(k==1, z=x; y=1; b=1; while(z>0, while(y<z, d=eulerphi(d); y++); b=2^b-floor((2^b-1)/d)*d; z=z-1; y=1; d=n); if(c==b, k=0); c=b; x++); x-2; }
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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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