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A173772
a(n) = (4*10^n + 23)/9.
4
7, 47, 447, 4447, 44447, 444447, 4444447, 44444447, 444444447, 4444444447, 44444444447, 444444444447, 4444444444447, 44444444444447, 444444444444447, 4444444444444447, 44444444444444447, 444444444444444447, 4444444444444444447, 44444444444444444447, 444444444444444444447
OFFSET
1,1
FORMULA
a(n) = 10*a(n-1) - 23 with n > 1, a(1) = 7.
a(n) = 11*a(n-1) - 10*a(n-2). G.f.: -x*(30*x-7)/((x-1)*(10*x-1)). [Colin Barker, Jan 24 2013]
E.g.f.: exp(x)*(4*exp(9*x) + 23)/9. - Elmo R. Oliveira, Sep 09 2024
MATHEMATICA
LinearRecurrence[{11, -10}, {7, 47}, 30] (* or *) Table[FromDigits[ PadLeft[ {7}, n, 4]], {n, 30}] (* Harvey P. Dale, Dec 27 2014 *)
PROG
(PARI) a(n)=4*10^n\9+3 \\ Charles R Greathouse IV, Jan 11 2012
CROSSREFS
Cf. A173771 (primes).
Sequence in context: A093173 A368177 A218761 * A178002 A288722 A006873
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Feb 24 2010
EXTENSIONS
a(19)-a(21) from Elmo R. Oliveira, Sep 09 2024
STATUS
approved