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%I #13 Dec 05 2017 21:20:01
%S 0,0,2,2,3,2,5,3,5,3,7,3,11,5,7,7,13,5,17,7,11,7,19,7,19,11,17,11,23,
%T 7,29,13,19,13,23,11,31,17,23,13,37,11,41,19,23,19,43,13,41,19,31,23,
%U 47,17,37,23,31,23,53,13,59,29,31,31,47,19,61,31,43,23,67,23,71,31,37,31
%N a(n) is the largest prime less than or equal to phi(n), a(1) = a(2) = 0.
%C The original name was: "Prime preceding phi(n)". However, this is true only for n >= 7 from which onward phi(n) is guaranteed to get only composite values. For n = 3, 4 and 6 for which phi(n) = 2, a(n) = 2 also.
%H Antti Karttunen, <a href="/A078773/b078773.txt">Table of n, a(n) for n = 1..16384</a>
%F a(1) = a(2) = 0 (by convention), and for n >= 3, a(n) = A007917(A000010(n)). - _Antti Karttunen_, Dec 05 2017
%e phi(10)=4, hence a(10)=3.
%t If[#<0,0,#]&/@Table[NextPrime[EulerPhi[n]+1,-1],{n,80}] (* _Harvey P. Dale_, Aug 10 2012 *)
%o (PARI) for (n=1,100, print1(precprime(eulerphi(n))","))
%Y Cf. A000010, A007917, A070800.
%K nonn
%O 1,3
%A _Jon Perry_, Jan 09 2003
%E Name changed by _Antti Karttunen_, Dec 05 2017
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