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A332150
a(n) = 5*(10^(2n+1)-1)/9 - 5*10^n.
9
0, 505, 55055, 5550555, 555505555, 55555055555, 5555550555555, 555555505555555, 55555555055555555, 5555555550555555555, 555555555505555555555, 55555555555055555555555, 5555555555550555555555555, 555555555555505555555555555, 55555555555555055555555555555, 5555555555555550555555555555555
OFFSET
0,2
FORMULA
a(n) = 5*A138148(n) = A002279(2n+1) - 5*10^n.
G.f.: 5*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.
MAPLE
A332150 := n -> 5*((10^(2*n+1)-1)/9-10^n);
MATHEMATICA
Array[5 ((10^(2 # + 1)-1)/9 - 10^#) &, 15, 0]
PROG
(PARI) apply( {A332150(n)=(10^(n*2+1)\9-10^n)*5}, [0..15])
(Python) def A332150(n): return (10**(n*2+1)//9-10**n)*5
CROSSREFS
Cf. A002275 (repunits R_n = (10^n-1)/9), A002279 (5*R_n), A011557 (10^n).
Cf. A138148 (cyclops numbers with binary digits), A002113 (palindromes).
Cf. A332120 .. A332190 (variants with different repeated digit 2, ..., 9).
Cf. A332151 .. A332159 (variants with different middle digit 1, ..., 9).
Sequence in context: A003791 A003925 A126846 * A336561 A158633 A204954
KEYWORD
nonn,base,easy
AUTHOR
M. F. Hasler, Feb 09 2020
STATUS
approved