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Search: id:A071615
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| A071615 |
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a(n) is the least m such that 2nm is a non-totient value, i.e. 2n*a(n) is in A005277. |
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+0
2
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| 7, 17, 15, 19, 5, 43, 1, 19, 5, 17, 7, 167, 1, 11, 3, 19, 1, 67, 1, 17, 17, 7, 5, 211, 1, 7, 11, 13, 3, 139, 1, 31, 9, 1, 5, 109, 1, 1, 3, 85, 3, 61, 1, 11, 1, 7, 1, 211, 1, 11, 5, 7, 3, 31, 5, 31, 1, 13, 1, 353, 1, 1, 9, 31, 3, 71, 1, 5, 3, 19, 1, 317, 1, 5, 3, 1, 1, 31, 1, 167, 7, 7, 5
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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n=5: number of terms in invphi(10k) is 2,5,2,9,0,9,... for k=1,2,3,...; a(5)=5 because 0 appears at 5th position.
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MAPLE
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with(numtheory); a := proc(n) local m; for m from 1 do if (invphi(2*n*m)=[]) then return m end end end
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MATHEMATICA
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invphi[n_, plist_] := Module[{i, p, e, pe, val}, If[plist=={}, Return[If[n==1, {1}, {}]]]; val={}; p=Last[plist]; For[e=0; pe=1, e==0||Mod[n, (p-1)pe/p]==0, e++; pe*=p, val=Join[val, pe*invphi[If[e==0, n, n*p/pe/(p-1)], Drop[plist, -1]]]]; Sort[val]]; invphi[n_] := invphi[n, Select[1+Divisors[n], PrimeQ]]; a[n_] := For[m=1, True, m++, If[invphi[2n*m]=={}, Return[m]]] (* invphi[n, plist] is list of x with phi(x)=n and all prime divisors of x in plist. *)
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CROSSREFS
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Cf. A000010, A005277, A002202, A071616.
Sequence in context: A089487 A107804 A128713 this_sequence A067459 A101240 A058887
Adjacent sequences: A071612 A071613 A071614 this_sequence A071616 A071617 A071618
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), May 27 2002
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EXTENSIONS
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Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), May 28 2002 and by Dean Hickerson (dean.hickerson(AT)yahoo.com), Jun 04 2002
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