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A332121
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a(n) = 2*(10^(2n+1)-1)/9 - 10^n.
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12
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1, 212, 22122, 2221222, 222212222, 22222122222, 2222221222222, 222222212222222, 22222222122222222, 2222222221222222222, 222222222212222222222, 22222222222122222222222, 2222222222221222222222222, 222222222222212222222222222, 22222222222222122222222222222, 2222222222222221222222222222222
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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.: (1 + 101*x - 300*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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A332121 := 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( {A332121(n)=10^(n*2+1)\9*2-10^n}, [0..15])
(Python) def A332121(n): return 10**(n*2+1)//9*2-10**n
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CROSSREFS
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Cf. A138148 (cyclops numbers with binary digits), A002113 (palindromes).
Cf. A332120 .. A332129 (variants with different middle digit 0, ..., 9).
Cf. A332131 .. A332191 (variants with different repeated digit 3, ..., 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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