

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
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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



FORMULA

a(n) = 2^(2*n + 2)  2^(n + 1)  2^n  1.
a(n) = 7*a(n1)14*a(n2)+8*a(n3). G.f.: 3*x*(4*x3) / ((x1)*(2*x1)*(4*x1)).  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**n2**(n+1)1),


CROSSREFS



KEYWORD

base,easy,nonn


AUTHOR



STATUS

approved



