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A304166
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a(n) = 972*n^2 - 1224*n + 414 with n > 0.
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2
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162, 1854, 5490, 11070, 18594, 28062, 39474, 52830, 68130, 85374, 104562, 125694, 148770, 173790, 200754, 229662, 260514, 293310, 328050, 364734, 403362, 443934, 486450, 530910, 577314, 625662, 675954, 728190, 782370, 838494, 896562, 956574, 1018530, 1082430, 1148274, 1216062, 1285794, 1357470, 1431090, 1506654
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OFFSET
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1,1
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COMMENTS
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a(n) provides the second Zagreb index of the HcDN1(n) network (see Fig. 3 in the Hayat et al. paper).
The second Zagreb index of a simple connected graph is the sum of the degree products d(i)d(j) over all edges ij of the graph.
The M-polynomial of HcDN1(n) is M(HcDN1(n); x,y) = 6x^3*y^3 + 12(n-1)x^3*y^5 + 6nx^3*y^6 + 18(n-1)x^5*y^6 + (27n^2 - 57n + 30)x^6*y^6. - Emeric Deutsch, May 11 2018
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LINKS
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FORMULA
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G.f.: 18*x*(9 + 76*x + 23*x^2)/(1 - x)^3.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 3. (End)
E.g.f.: 18*(exp(x)*(23 - 14*x + 54*x^2) - 23). - Stefano Spezia, Apr 15 2023
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MAPLE
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seq(972*n^2-1224*n+414, n = 1 .. 40);
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PROG
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(PARI) a(n) = 972*n^2-1224*n+414; \\ Altug Alkan, May 09 2018
(PARI) Vec(18*x*(9 + 76*x + 23*x^2) / (1 - x)^3 + O(x^60)) \\ Colin Barker, May 10 2018
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CROSSREFS
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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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