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A332193
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a(n) = 10^(2n+1) - 1 - 6*10^n.
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7
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3, 939, 99399, 9993999, 999939999, 99999399999, 9999993999999, 999999939999999, 99999999399999999, 9999999993999999999, 999999999939999999999, 99999999999399999999999, 9999999999993999999999999, 999999999999939999999999999, 99999999999999399999999999999, 9999999999999993999999999999999
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listen;
history;
text;
internal format)
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OFFSET
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0,1
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LINKS
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FORMULA
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G.f.: (3 + 606*x - 1500*x^2)/((1 - x)(1 - 10*x)(1 - 100*x)).
a(n) = 111*a(n-1) - 1110*a(n-2) + 1000*a(n-3) for n > 2.
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MAPLE
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A332193 := n -> 10^(n*2+1)-1-6*10^n;
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MATHEMATICA
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Array[ 10^(2 # + 1) - 1 - 6*10^# &, 15, 0]
LinearRecurrence[{111, -1110, 1000}, {3, 939, 99399}, 20] (* Harvey P. Dale, Jan 19 2024 *)
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PROG
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(PARI) apply( {A332193(n)=10^(n*2+1)-1-6*10^n}, [0..15])
(Python) def A332193(n): return 10**(n*2+1)-1-6*10^n
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CROSSREFS
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Cf. A138148 (cyclops numbers with binary digits only), A002113 (palindromes).
Cf. A332113 .. A332183 (variants with different repeated digit 1, ..., 8).
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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