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 A146509 Numbers that are congruent to {1, 5} mod 18. 5
 1, 5, 19, 23, 37, 41, 55, 59, 73, 77, 91, 95, 109, 113, 127, 131, 145, 149, 163, 167, 181, 185, 199, 203, 217, 221, 235, 239, 253, 257, 271, 275, 289, 293, 307, 311, 325, 329, 343, 347, 361, 365, 379, 383, 397, 401, 415, 419, 433, 437, 451, 455, 469, 473, 487 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Positive integers k such that Hypergeometric[k/6,(6-k)/6,1/2,3/4] = 2Cos[2Pi/9]. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (1, 1, -1). FORMULA a(2k-1) = 18*(k-1)+1, a(2k) = 18*(k-1)+5, where k>0. G.f.: x*(1+4*x+13*x^2)/((1+x)*(1-x)^2). - Vincenzo Librandi, Jul 11 2012 a(n) = (18*n-5*(-1)^n+21)/2. - Bruno Berselli, Jul 12 2012 a(1)=1, a(n) = 18*n -a(n-1) -30. - Vincenzo Librandi, Jul 12 2012 MATHEMATICA Select[Range[500], MemberQ[{1, 5}, Mod[#, 18]]&] (* Harvey P. Dale, Jul 24 2011 *) PROG (MAGMA) [n: n in [1..500] | n mod 18 in [1, 5]]; // Bruno Berselli, Jul 12 2012 (PARI) a(n)=n\2*18+if(n%2, 1, -13) \\ Charles R Greathouse IV, Jul 14 2012 CROSSREFS Cf. A146507, A146511, A146512. Sequence in context: A097934 A191609 A191084 * A062340 A167766 A106957 Adjacent sequences:  A146506 A146507 A146508 * A146510 A146511 A146512 KEYWORD nonn,easy AUTHOR Artur Jasinski, Oct 30 2008 EXTENSIONS Crossrefs corrected by Ray Chandler, Dec 06 2016 STATUS approved

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Last modified October 14 00:10 EDT 2019. Contains 327990 sequences. (Running on oeis4.)