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 A220236 Binary palindromic numbers with only two 0 bits, both in the middle. 2
 9, 51, 231, 975, 3999, 16191, 65151, 261375, 1047039, 4191231, 16771071, 67096575, 268410879, 1073692671, 4294868991, 17179672575, 68719083519, 274877120511, 1099510054911, 4398043365375, 17592179752959, 70368731594751, 281474951544831, 1125899856510975 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Binary expansion is 1001, 110011, 11100111, 1111001111, ... Last digit of the decimal representation follows the pattern 9, 1, 1, 5, 9, 1, 1, 5, 9, ... LINKS Table of n, a(n) for n=1..24. Index entries for linear recurrences with constant coefficients, signature (7,-14,8). FORMULA a(n) = 2^(2*n + 2) - 2^(n + 1) - 2^n - 1. a(n) = 7*a(n-1)-14*a(n-2)+8*a(n-3). G.f.: 3*x*(4*x-3) / ((x-1)*(2*x-1)*(4*x-1)). - Colin Barker, May 31 2013 MATHEMATICA Table[2^(2n + 2) - 2^(n + 1) - 2^n - 1, {n, 25}] (* Alonso del Arte, Dec 08 2012 *) LinearRecurrence[{7, -14, 8}, {9, 51, 231}, 30] (* Harvey P. Dale, Jan 24 2019 *) PROG (Python) for n in range(1, 77): print (2**(2*n+2)-2**n-2**(n+1)-1), CROSSREFS Cf. A129868. Sequence in context: A055900 A054549 A005746 * A345954 A061178 A246178 Adjacent sequences: A220233 A220234 A220235 * A220237 A220238 A220239 KEYWORD base,easy,nonn AUTHOR Alex Ratushnyak, Dec 08 2012 STATUS approved

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Last modified December 8 08:02 EST 2023. Contains 367662 sequences. (Running on oeis4.)