|
%I #9 Mar 30 2012 18:34:53
%S 2,1,1,2,1,4,3,4,3,5,5,8,26,7,5,8,9,12,5,10,7,8,46,16,5,13,9,14,7,25,
%T 21,13,9,17,7,24,62,19,11,20,76,28,13,16,15,23,17,32,21,25,17,26,52,
%U 36,11,28,13,26,13,45,74,28,17,26,13,39,33,31,21,32,13,48,39,37,25,38
%N Smallest k such that phi(k+n)=2*phi(k).
%C Makowski proved that the sequence is well-defined.
%C It appears that k<=2n, with equality for the n in A110196 only. Computations for n<10^6 appear to show that k<n for all but a finite number of n. - _T. D. Noe_, Jul 15 2005
%D R. K. Guy, Unsolved Problems Number Theory, Sect. B36
%e phi(13+26)=24=2*phi(13), so a(13) is 26.
%t Table[k=1; While[EulerPhi[n+k] != 2*EulerPhi[k], k++ ]; k, {n, 100}] (Noe)
%Y Cf. A000010, A007015, A050472.
%Y Cf. A110179 (least k such that phi(n+k)=2*phi(n)).
%K nonn
%O 1,1
%A _Jud McCranie_, Dec 24 1999
|
