A071616 Smallest even number divisible by 2n which is nontotient, i.e., in A005277.
14, 68, 90, 152, 50, 516, 14, 304, 90, 340, 154, 4008, 26, 308, 90, 608, 34, 2412, 38, 680, 714, 308, 230, 10128, 50, 364, 594, 728, 174, 8340, 62, 1984, 594, 68, 350, 7848, 74, 76, 234, 6800, 246, 5124, 86, 968, 90, 644, 94, 20256, 98, 1100, 510, 728, 318
Offset: 1
Keywords
Examples
n=4: 2n=8 and number of terms in invphi(8k) is 5, 6, 10, 7, 9, 11, 3, 8, 17, 10, 6, 17, 3, 6, 17, 9, 9, 21, 0, 12, ... for k=1,2,...,20,...; zero appears first at k=19, so a(4) = 8k = 152.
Links
- Donovan Johnson, Table of n, a(n) for n = 1..10000
Programs
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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[2n*m]]] (* invphi[n, plist] is list of x with phi(x)=n and all prime divisors of x in plist. *)
Extensions
Edited and extended by Robert G. Wilson v, May 28 2002 and by Dean Hickerson, Jun 04 2002
Comments