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A332152
a(n) = 5*(10^(2*n+1)-1)/9 - 3*10^n.
1
2, 525, 55255, 5552555, 555525555, 55555255555, 5555552555555, 555555525555555, 55555555255555555, 5555555552555555555, 555555555525555555555, 55555555555255555555555, 5555555555552555555555555, 555555555555525555555555555, 55555555555555255555555555555, 5555555555555552555555555555555
OFFSET
0,1
FORMULA
a(n) = 5*A138148(n) + 2*10^n = A002279(2n+1) - 3*10^n.
G.f.: (2 + 303*x - 800*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
A332152 := n -> 5*(10^(2*n+1)-1)/9-3*10^n;
MATHEMATICA
Array[5 (10^(2 # + 1)-1)/9 - 3*10^# &, 15, 0]
PROG
(PARI) apply( {A332152(n)=10^(n*2+1)\9*5-3*10^n}, [0..15])
(Python) def A332152(n): return 10**(n*2+1)//9*5-3*10**n
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. A332112 .. A332192 (variants with different repeated digit 1, ..., 9).
Cf. A332150 .. A332159 (variants with different middle digit 0, ..., 9).
Sequence in context: A283756 A352803 A071613 * A262649 A202277 A177836
KEYWORD
nonn,base,easy
AUTHOR
M. F. Hasler, Feb 09 2020
STATUS
approved