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%I #16 Jul 10 2017 02:34:21
%S 1,2,2,2,2,2,4,2,2,2,2,4,2,2,4,4,2,2,2,2,4,2,2,2,2,4,2,4,2,6,2,2,2,4,
%T 4,4,4,2,2,2,2,2,2,4,4,6,2,2,2,4,2,2,4,4,2,6,4,2,2,2,2,4,4,2,2,4,6,2,
%U 4,2,2,4,4,2,2,4,4,2,2,2,2,4,6,2,10,2,4,4,2,2,4,2,2,4,4,2,6,4,2,2,4,6,4,2,4
%N First difference sequence of A002202. Difference between consecutive possible values for phi(n).
%H Reinhard Zumkeller, <a href="/A083533/b083533.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A002202(n+1) - A002202(n).
%e 12 and 16 are the 7th and 8th possible totient values 12 = phi(13), 16 = phi(17),
%e while {13,14,15} are impossible ones; thus 16 - 12 = 4 = a(7) = A002202(8) - A002202(7).
%t t=Table[EulerPhi[w], {w, 1, 25000}]; u=Union[%]; Delete[u-RotateRight[u], 1]
%o (Haskell)
%o a083533 n = a083533_list !! (n-1)
%o a083533_list = zipWith (-) (tail a002202_list) a002202_list
%o -- _Reinhard Zumkeller_, Nov 26 2015
%Y Cf. A000010, A002202, A005277, A083531, A083532, A083534, A083535, A083536, A005277.
%K nonn
%O 1,2
%A _Labos Elemer_, May 20 2003
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