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A332187
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a(n) = 8*(10^(2n+1)-1)/9 - 10^n.
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3
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7, 878, 88788, 8887888, 888878888, 88888788888, 8888887888888, 888888878888888, 88888888788888888, 8888888887888888888, 888888888878888888888, 88888888888788888888888, 8888888888887888888888888, 888888888888878888888888888, 88888888888888788888888888888, 8888888888888887888888888888888
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listen;
history;
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internal format)
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OFFSET
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0,1
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LINKS
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Table of n, a(n) for n=0..15.
Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).
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FORMULA
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a(n) = 8*A138148(n) + 7*10^n = A002282(2n+1) - 10^n.
G.f.: (7 + 101*x - 900*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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A332187 := n -> 8*(10^(2*n+1)-1)/9-10^n;
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MATHEMATICA
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Array[8 (10^(2 # + 1)-1)/9 - 10^# &, 15, 0]
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PROG
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(PARI) apply( {A332187(n)=10^(n*2+1)\9*8-10^n}, [0..15])
(Python) def A332187(n): return 10**(n*2+1)//9*8-10**n
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CROSSREFS
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Cf. (A077776-1)/2 = A183190: indices of primes.
Cf. A002275 (repunits R_n = (10^n-1)/9), A002282 (8*R_n), A011557 (10^n).
Cf. A138148 (cyclops numbers with binary digits only), A002113 (palindromes).
Cf. A332117 .. A332197 (variants with different "wing" digit 1, ..., 9).
Cf. A332180 .. A332189 (variants with different middle digit 0, ..., 9).
Sequence in context: A308296 A193342 A298301 * A093171 A330295 A177908
Adjacent sequences: A332184 A332185 A332186 * A332188 A332189 A332190
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KEYWORD
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nonn,base,easy
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AUTHOR
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M. F. Hasler, Feb 08 2020
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STATUS
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approved
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