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A050520 Values of phi in arithmetic progression of at least 6 terms having the same value of phi in A050518.

%I A050520 #32 May 14 2015 23:25:27
%S A050520 155520,311040,466560,622080,777600,933120,933120,1244160,1399680,
%T A050520 1555200,1555200,1866240,1866240,1866240,2332800,2488320,2488320,
%U A050520 2799360,2799360,3110400,2799360,3110400,3421440,3732480,3888000
%N A050520 Values of phi in arithmetic progression of at least 6 terms having the same value of phi in A050518.
%C A050520 The values of phi for terms between 13413600 and 10^9 (see comment on A050518) are 3732480, 3888000, 3732480, 4199040, 3732480, 4354560, 4665600, 4665600, 4976640, 4665600, 14999040, 19595520, 29998080, 44130240, 39191040, 44997120, 58786560, 59996160, 88260480, 78382080, 132390720, 134648640, 145313280, 176520960, 220651200, 237948480, 264781440. - _Mauro Fiorentini_, Apr 17 2015
%H A050520 Robert Israel, <a href="/A050520/b050520.txt">Table of n, a(n) for n = 1..114</a>
%H A050520 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/NonRecursions.html">Non Recursions</a>
%p A050520 N:= 10^7: # to get all terms <= N in A050518
%p A050520 with(numtheory):
%p A050520 Res:= NULL:
%p A050520 phis:= {seq(phi(i), i=2..N)}:
%p A050520 for m in phis do
%p A050520    S:= convert(invphi(m), set);
%p A050520    if nops(S) < 6 then next fi;
%p A050520    for d from 0 to 4 do
%p A050520      Sd[d]:= select(t-> (t mod 5 = d), S, d);
%p A050520      nd:= nops(Sd[d]);
%p A050520      for i0 from 1 to nd-1 do
%p A050520        s0:= Sd[d][i0];
%p A050520        if s0 > N then break fi;
%p A050520        for i5 from i0+1 to nd do
%p A050520          s5:= Sd[d][i5];
%p A050520          incr:= (s5 - s0)/5;
%p A050520          if {s0+incr, s0+2*incr, s0+3*incr, s0+4*incr} subset S then
%p A050520            Res:= Res, [s0, m];
%p A050520          fi
%p A050520        od
%p A050520      od;
%p A050520    od;
%p A050520 od:
%p A050520 map2(op,2,sort([Res], (s, t)->s[1]<t[1])); # _Robert Israel_, May 10 2015
%Y A050520 Cf. A000010, A050495, A050496, A050497, A050515-A050520.
%K A050520 nonn
%O A050520 1,1
%A A050520 _Jud McCranie_, Dec 28 1999