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A332125
a(n) = 2*(10^(2n+1)-1)/9 + 3*10^n.
3
5, 252, 22522, 2225222, 222252222, 22222522222, 2222225222222, 222222252222222, 22222222522222222, 2222222225222222222, 222222222252222222222, 22222222222522222222222, 2222222222225222222222222, 222222222222252222222222222, 22222222222222522222222222222, 2222222222222225222222222222222
OFFSET
0,1
FORMULA
a(n) = 2*A138148(n) + 5*10^n = A002276(2n+1) + 3*10^n.
G.f.: (5 - 303*x + 100*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
A332125 := n -> 2*(10^(2*n+1)-1)/9+3*10^n;
MATHEMATICA
Array[2 (10^(2 # + 1)-1)/9 + 3*10^# &, 15, 0]
PROG
(PARI) apply( {A332125(n)=10^(n*2+1)\9*2+3*10^n}, [0..15])
(Python) def A332125(n): return 10**(n*2+1)//9*2+3*10**n
CROSSREFS
Cf. A002275 (repunits R_n = (10^n-1)/9), A002276 (2*R_n), A011557 (10^n).
Cf. A138148 (cyclops numbers with binary digits), A002113 (palindromes).
Cf. A332115 .. A332195 (variants with different repeated digit 1, ..., 9).
Cf. A332120 .. A332129 (variants with different middle digit 0, ..., 9).
Sequence in context: A308295 A060943 A336295 * A308652 A002770 A069071
KEYWORD
nonn,base,easy
AUTHOR
M. F. Hasler, Feb 09 2020
STATUS
approved