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a(n) is the number of terms in the expansion of (x+y-z)*(x^2+y^2-z^2)*(x^3+y^3-z^3)*...*(x^n+y^n-z^n).
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%I #7 Oct 02 2018 16:37:23

%S 3,9,22,48,102,182,328,566,910,1396,2025,2882,3976,5304,7002,9071,

%T 11475,14444,17886,21896,26531,31880,37947,44899,52657,61500,71406,

%U 82383,94592,108097,123017,139401,157439,177134,198634,221962,247378,274767,304483,336533,371083,408168,447944,490614,536208

%N a(n) is the number of terms in the expansion of (x+y-z)*(x^2+y^2-z^2)*(x^3+y^3-z^3)*...*(x^n+y^n-z^n).

%p P:= 1;

%p for n from 1 to 90 do

%p P:= expand(P*(x^n+y^n-z^n));

%p A[n]:= nops(P);

%p od:

%p seq(A[n],n=1..90); # _Robert Israel_, Apr 14 2017

%t Table[Length[Expand[Times@@Table[x^n+y^n-z^n,{n,i}]]],{i,50}] (* _Harvey P. Dale_, Oct 02 2018 *)

%Y Cf. A086796.

%K nonn

%O 1,1

%A Yuval Dekel (dekelyuval(AT)hotmail.com), Aug 06 2003

%E a(12)-a(45) from _Robert Israel_, Apr 14 2017