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 A326490 Number of subsets of {1..n} containing no differences or quotients of pairs of distinct elements. 5
 1, 2, 3, 5, 7, 12, 18, 31, 46, 72, 102, 172, 259, 428, 607, 989, 1329, 2142, 3117, 4953, 6956, 11032, 15321, 23979, 33380, 48699, 66849, 104853, 144712, 220758, 304133, 461580, 636556, 973843, 1316513, 1958828, 2585433, 3882843, 5237093, 7884277, 10555739, 15729293 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS FORMULA For n > 0, a(n) = A326495(n) + 1. EXAMPLE The a(0) = 1 through a(6) = 18 subsets:   {}  {}   {}   {}     {}     {}       {}       {1}  {1}  {1}    {1}    {1}      {1}            {2}  {2}    {2}    {2}      {2}                 {3}    {3}    {3}      {3}                 {2,3}  {4}    {4}      {4}                        {2,3}  {5}      {5}                        {3,4}  {2,3}    {6}                               {2,5}    {2,3}                               {3,4}    {2,5}                               {3,5}    {2,6}                               {4,5}    {3,4}                               {3,4,5}  {3,5}                                        {4,5}                                        {4,6}                                        {5,6}                                        {2,5,6}                                        {3,4,5}                                        {4,5,6} MATHEMATICA Table[Length[Select[Subsets[Range[n]], Intersection[#, Union[Divide@@@Reverse/@Subsets[#, {2}], Subtract@@@Reverse/@Subsets[#, {2}]]]=={}&]], {n, 0, 10}] PROG (PARI) a(n)={    my(recurse(k, b)=     if(k > n, 1,       my(t = self()(k + 1, b));       for(i=1, k\2, if(bittest(b, i) && (bittest(b, k-i) || (!(k%i) && bittest(b, k/i))), return(t)));       t += self()(k + 1, b + (1<

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Last modified October 1 04:06 EDT 2020. Contains 337441 sequences. (Running on oeis4.)