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A264293 Number of irreducible polynomials in the n-th generation of polynomials generated as in Comments. 0

%I #16 Nov 24 2018 01:28:19

%S 0,0,2,4,9,20,54,131,354,912,2457,6429,17081,44850,118578,311471

%N Number of irreducible polynomials in the n-th generation of polynomials generated as in Comments.

%C The set of polynomials T is generated by these rules: 0 is in T, and if p is in T, then p + 1 is in T and x*p is in T and y*p is in T. The n-th generation of T consists of F(2n) polynomials, for n >= 0, where F = A000045 = Fibonacci numbers.

%C Note that a given polynomial can appear only once; e.g., though x*y can arise either from multiplying x by y or y by x, it occurs only once in generation 3. Also although 0*x = 0, 0 occurs only in generation 0. - _Robert Israel_, Nov 22 2018

%e First few generations:

%e g(0) = {0}

%e g(1) = {1}

%e g(2) = {2,x,y}

%e g(3) = {3, 2x, x^2, 1+x, 2y, xy, y^2, 1+y}

%e The irreducible polynomials in g(3) are 2x, 1+x, 2y, 1+y, so that a(3) = 4.

%p A[0]:= 0: A[1]:= 0:

%p T:= {1}:

%p for n from 2 to 13 do

%p T:= map(t -> (t+1,expand(x*t),expand(y*t)),T);

%p A[n]:= nops(select(irreduc,T));

%p od:

%p seq(A[i],i=0..13); # _Robert Israel_, Nov 22 2018

%t z = 12; t = Expand[NestList[DeleteDuplicates[Flatten[Map[{# + 1, x*#, y*#} &, #], 1]] &, {0}, z]];

%t s[0] = t[[1]]; s[n_] := s[n] = Union[t[[n]], s[n - 1]]

%t g[n_] := Complement[s[n], s[n - 1]]

%t Table[Length[g[z]], {z, 1, z}]

%t Column[Table[g[z], {z, 1, 6}]]

%t Table[Count[Map[IrreduciblePolynomialQ, g[n]], True], {n, 1, z}]

%Y Cf. A001906, A262841, A264292.

%K nonn,more

%O 0,3

%A _Clark Kimberling_, Nov 24 2015

%E Edited, and a(12)-a(15) from _Robert Israel_, Nov 22 2018

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Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)