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A301291
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Expansion of (x^4+3*x^3+x^2+3*x+1)/((x^2+1)*(x-1)^2).
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38
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1, 5, 9, 13, 18, 23, 27, 31, 36, 41, 45, 49, 54, 59, 63, 67, 72, 77, 81, 85, 90, 95, 99, 103, 108, 113, 117, 121, 126, 131, 135, 139, 144, 149, 153, 157, 162, 167, 171, 175, 180, 185, 189, 193, 198, 203, 207, 211, 216, 221, 225, 229, 234, 239, 243, 247, 252
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OFFSET
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0,2
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COMMENTS
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Appears to be coordination sequence for node of type 3^3.4^2 in "krm" 2-D tiling (or net).
Also appears to be coordination sequence for pentavalent node in "krk" 2-D tiling (or net).
Linear recurrence and g.f. confirmed by Shutov/Maleev link. - Ray Chandler, Aug 30 2023
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REFERENCES
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Branko Grünbaum and G. C. Shephard, Tilings and Patterns. W. H. Freeman, New York, 1987. See Table 2.2.1, page 67, row 3, first tiling; also p. 66, row 3, first tiling.
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LINKS
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FORMULA
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For explicit formula for a(n) see Maple code.
a(n) = 2*a(n-1) - 2*a(n-2) + 2*a(n-3) - a(n-4) for n > 4. - Colin Barker, Mar 23 2018
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MAPLE
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f:=proc(n) if n=0 then 1
elif (n mod 2) = 0 then 9*n/2
elif (n mod 4) = 1 then 18*(n-1)/4+5
else 18*(n-3)/4+13; fi; end;
s1:=[seq(f(n), n=0..60)];
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MATHEMATICA
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Join[{1}, LinearRecurrence[{2, -2, 2, -1}, {5, 9, 13, 18}, 60]] (* Jean-François Alcover, Jan 08 2019 *)
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PROG
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(PARI) Vec((x^4+3*x^3+x^2+3*x+1)/((x^2+1)*(x-1)^2) + O(x^60)) \\ Colin Barker, Mar 23 2018
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CROSSREFS
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Coordination sequences for the 20 2-uniform tilings in the order in which they appear in the Galebach catalog, together with their names in the RCSR database (two sequences per tiling): #1 krt A265035, A265036; #2 cph A301287, A301289; #3 krm A301291, A301293; #4 krl A301298, A298024; #5 krq A301299, A301301; #6 krs A301674, A301676; #7 krr A301670, A301672; #8 krk A301291, A301293; #9 krn A301678, A301680; #10 krg A301682, A301684; #11 bew A008574, A296910; #12 krh A301686, A301688; #13 krf A301690, A301692; #14 krd A301694, A219529; #15 krc A301708, A301710; #16 usm A301712, A301714; #17 krj A219529, A301697; #18 kre A301716, A301718; #19 krb A301720, A301722; #20 kra A301724, A301726.
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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