A071615 a(n) is the least m such that 2*n*m is a nontotient value; that is, 2*n*a(n) is in A005277.

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

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

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.

Maple

with(numtheory); a := proc(n) local m; for m from 1 do if (invphi(2*n*m)=[]) then return m end end end

Mathematica

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. *)

Crossrefs

Cf. A000010, A005277, A002202, A071616.

Sequence in context: A128713 A283163 A196164 * A067459 A323746 A101240

Adjacent sequences: A071612 A071613 A071614 * A071616 A071617 A071618

Keyword

nonn

Author

Labos Elemer, May 27 2002

Extensions

Edited and extended by Robert G. Wilson v, May 28 2002

Edited and extended by Dean Hickerson, Jun 04 2002

Status

approved