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A194717
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Number of n-ary words beginning with the first character of the alphabet, that can be built by inserting five doublets into the initially empty word.
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2
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0, 1, 126, 1181, 4966, 14289, 32966, 65821, 118686, 198401, 312814, 470781, 682166, 957841, 1309686, 1750589, 2294446, 2956161, 3751646, 4697821, 5812614, 7114961, 8624806, 10363101, 12351806, 14613889, 17173326, 20055101, 23285206, 26890641, 30899414, 35340541
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OFFSET
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0,3
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LINKS
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FORMULA
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G.f.: -x*(1+121*x+561*x^2+311*x^3+14*x^4) / (x-1)^5.
a(0) = 0, a(n) = 1+(8+(27+(48+42*(n-1))*(n-1))*(n-1))*(n-1) for n>0.
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EXAMPLE
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a(1) = 1: aaaaaaaaaa (with 1-ary alphabet {a}).
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MAPLE
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a:= n-> `if`(n=0, 0, (x-> 1+(8+(27+(48+42*x)*x)*x)*x)(n-1)):
seq(a(n), n=0..40);
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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