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A332181
a(n) = 8*(10^(2n+1)-1)/9 - 7*10^n.
3
1, 818, 88188, 8881888, 888818888, 88888188888, 8888881888888, 888888818888888, 88888888188888888, 8888888881888888888, 888888888818888888888, 88888888888188888888888, 8888888888881888888888888, 888888888888818888888888888, 88888888888888188888888888888, 8888888888888881888888888888888
OFFSET
0,2
FORMULA
a(n) = 8*A138148(n) + 10^n = A002282(2n+1) - 7*10^n.
G.f.: (1 + 707*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.
MAPLE
A332181 := n -> 8*(10^(2*n+1)-1)/9-7*10^n;
MATHEMATICA
Array[8 (10^(2 # + 1)-1)/9 - 7*10^# &, 15, 0]
PROG
(PARI) apply( {A332181(n)=10^(n*2+1)\9*8-7*10^n}, [0..15])
(Python) def A332181(n): return 10**(n*2+1)//9*8-7*10**n
CROSSREFS
Cf. (A077776-1)/2 = A183184: 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).
Cf. A332121 .. A332191 (variants with different repeated digit 2, ..., 9).
Cf. A332180 .. A332189 (variants with different middle digit 0, ..., 9).
Sequence in context: A279441 A221748 A105989 * A266059 A356414 A020445
KEYWORD
nonn,base,easy
AUTHOR
M. F. Hasler, Feb 08 2020
STATUS
approved