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A050520 Values of phi in arithmetic progression of at least 6 terms having the same value of phi in A050518. 6
155520, 311040, 466560, 622080, 777600, 933120, 933120, 1244160, 1399680, 1555200, 1555200, 1866240, 1866240, 1866240, 2332800, 2488320, 2488320, 2799360, 2799360, 3110400, 2799360, 3110400, 3421440, 3732480, 3888000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Robert Israel, Table of n, a(n) for n = 1..114

Tanya Khovanova, Non Recursions

MAPLE

N:= 10^7: # to get all terms <= N in A050518

with(numtheory):

Res:= NULL:

phis:= {seq(phi(i), i=2..N)}:

for m in phis do

   S:= convert(invphi(m), set);

   if nops(S) < 6 then next fi;

   for d from 0 to 4 do

     Sd[d]:= select(t-> (t mod 5 = d), S, d);

     nd:= nops(Sd[d]);

     for i0 from 1 to nd-1 do

       s0:= Sd[d][i0];

       if s0 > N then break fi;

       for i5 from i0+1 to nd do

         s5:= Sd[d][i5];

         incr:= (s5 - s0)/5;

         if {s0+incr, s0+2*incr, s0+3*incr, s0+4*incr} subset S then

           Res:= Res, [s0, m];

         fi

       od

     od;

   od;

od:

map2(op, 2, sort([Res], (s, t)->s[1]<t[1])); # Robert Israel, May 10 2015

CROSSREFS

Cf. A000010, A050495, A050496, A050497, A050515-A050520.

Sequence in context: A282163 A250883 A233816 * A049443 A228473 A156118

Adjacent sequences:  A050517 A050518 A050519 * A050521 A050522 A050523

KEYWORD

nonn

AUTHOR

Jud McCranie, Dec 28 1999

STATUS

approved

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Last modified December 10 18:10 EST 2019. Contains 329901 sequences. (Running on oeis4.)