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A332120
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a(n) = 2*(10^(2n+1)-1)/9 - 2*10^n.
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16
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0, 202, 22022, 2220222, 222202222, 22222022222, 2222220222222, 222222202222222, 22222222022222222, 2222222220222222222, 222222222202222222222, 22222222222022222222222, 2222222222220222222222222, 222222222222202222222222222, 22222222222222022222222222222, 2222222222222220222222222222222
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: 2*x*(101 - 200*x)/((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.
E.g.f.: 2*exp(x)*(10*exp(99*x) - 9*exp(9*x) - 1)/9. - Stefano Spezia, Jul 13 2024
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MAPLE
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A332120 := n -> 2*((10^(2*n+1)-1)/9-10^n);
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MATHEMATICA
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Array[2 ((10^(2 # + 1)-1)/9 - 10^#) &, 15, 0]
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PROG
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(PARI) apply( {A332120(n)=(10^(n*2+1)\9-10^n)*2}, [0..15])
(Python) def A332120(n): return (10**(n*2+1)//9-10**n)*2
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CROSSREFS
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Cf. A138148 (cyclops numbers with binary digits), A002113 (palindromes).
Cf. A332130 .. A332190 (variants with different repeated digit 3, ..., 9).
Cf. A332121 .. A332129 (variants with different middle digit 1, ..., 9).
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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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