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A332191
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a(n) = 10^(2n+1) - 1 - 8*10^n.
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9
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1, 919, 99199, 9991999, 999919999, 99999199999, 9999991999999, 999999919999999, 99999999199999999, 9999999991999999999, 999999999919999999999, 99999999999199999999999, 9999999999991999999999999, 999999999999919999999999999, 99999999999999199999999999999, 9999999999999991999999999999999
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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COMMENTS
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See A183184 = {1, 5, 13, 43, 169, 181, ...} for the indices of primes.
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LINKS
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FORMULA
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G.f.: (1 + 808*x - 1700*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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A332191 := n -> 10^(n*2+1)-1-8*10^n;
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MATHEMATICA
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Array[ 10^(2 # + 1)-1-8*10^# &, 15, 0]
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PROG
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(PARI) apply( {A332191(n)=10^(n*2+1)-1-8*10^n}, [0..15])
(Python) def A332191(n): return 10**(n*2+1)-1-8*10^n
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CROSSREFS
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Cf. A138148 (cyclops numbers with binary digits only), A002113 (palindromes).
Cf. A332121 .. A332181 (variants with different repeated digit 2, ..., 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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