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A298123
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Number of connected induced subgraphs in the n-Apollonian network.
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2
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OFFSET
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1,1
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COMMENTS
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Term a(6) has 108 decimal digits and a(7) has 323 decimal digits. - Andrew Howroyd, Jan 16 2018
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LINKS
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MATHEMATICA
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{1, 3, 3, 1} . # & /@ NestList[Function[{t0, t1, t2, t3}, {3 t0 + t1^3, t1^2 + t1 t2^2, t1^2 t2 + t2^2 t3, t2^3 + t3^3}] @@ # &, {1, 2, 2, 2}, 4] (* Eric W. Weisstein, Jan 17 2018 *)
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PROG
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(PARI) \\ here t0..t3 are for 0..3 outside vertices included in set.
D(t0, t1, t2, t3)={[3*t0 + t1^3, t1^2 + t1*t2^2, t1^2*t2 + t2^2*t3, t2^3 + t3^3]}
a(n)={my(v=[1, 2, 2, 2]); for(i=2, n, v=D(v[1], v[2], v[3], v[4])); v[1]+3*v[2]+3*v[3]+v[4]} \\ Andrew Howroyd, Jan 16 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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