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 A069507 a(1) = 4; a(n) = smallest palindromic number of the form k*a(n-1) + 1 with k > 1. 6
 4, 9, 55, 111, 1111, 11111, 111111, 1111111, 11111111, 111111111, 1111111111, 11111111111, 111111111111, 1111111111111, 11111111111111, 111111111111111, 1111111111111111, 11111111111111111, 111111111111111111 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 FORMULA a(n) = {10^(n-1)-1}/9 for n > 3. From Chai Wah Wu, Jun 20 2016: (Start) a(n) = 11*a(n-1) - 10*a(n-2) for n > 4. G.f.: (440*x^4 - 404*x^3 - 4*x^2 - 35*x + 4)/((x - 1)*(10*x - 1)). (End) MATHEMATICA CoefficientList[Series[(440 x^4 - 404 x^3 - 4 x^2 - 35 x + 4) / ((x - 1) (10 x - 1)), {x, 0, 30}], x] (* Vincenzo Librandi, Jun 21 2016 *) PROG (MAGMA) I:=[4, 9, 55, 111, 1111]; [n le 5 select I[n] else 11*Self(n-1)-10*Self(n-2): n in [1..25]]; // Vincenzo Librandi, Jun 21 2016 CROSSREFS Cf. A069505, A069506, A069508, A069509, A069510. Sequence in context: A009276 A086692 A242036 * A219894 A203464 A152284 Adjacent sequences:  A069504 A069505 A069506 * A069508 A069509 A069510 KEYWORD nonn,base AUTHOR Amarnath Murthy, Mar 30 2002 EXTENSIONS More terms from Patrick De Geest, Jun 11 2003 STATUS approved

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Last modified January 15 19:23 EST 2019. Contains 319171 sequences. (Running on oeis4.)