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A332148
a(n) = 4*(10^(2*n+1)-1)/9 + 4*10^n.
2
8, 484, 44844, 4448444, 444484444, 44444844444, 4444448444444, 444444484444444, 44444444844444444, 4444444448444444444, 444444444484444444444, 44444444444844444444444, 4444444444448444444444444, 444444444444484444444444444, 44444444444444844444444444444, 4444444444444448444444444444444
OFFSET
0,1
FORMULA
a(n) = 4*A138148(n) + 8*10^n = A002278(2n+1) + 4*10^n = 4*A332112(n).
G.f.: (8 - 404*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
A332148 := n -> 4*((10^(2*n+1)-1)/9+10^n);
MATHEMATICA
Array[4 ((10^(2 # + 1)-1)/9 + 10^#) &, 15, 0]
PROG
(PARI) apply( {A332148(n)=(10^(n*2+1)\9+10^n)*4}, [0..15])
(Python) def A332148(n): return (10**(n*2+1)//9+10**n)*4
CROSSREFS
Cf. A002275 (repunits R_n = (10^n-1)/9), A002278 (4*R_n), A011557 (10^n).
Cf. A138148 (cyclops numbers with binary digits), A002113 (palindromes).
Cf. A332118 .. A332178, A181965 (variants with different repeated digit 1, ..., 9).
Cf. A332140 .. A332149 (variants with different middle digit 0, ..., 9).
Sequence in context: A204564 A152495 A197096 * A109060 A259926 A282180
KEYWORD
nonn,base,easy
AUTHOR
M. F. Hasler, Feb 09 2020
STATUS
approved