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A029750
List of numbers of the form 2^k times 1, 3, 5 or 7.
20
1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, 20, 24, 28, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, 448, 512, 640, 768, 896, 1024, 1280, 1536, 1792, 2048, 2560, 3072, 3584, 4096, 5120, 6144, 7168, 8192, 10240
OFFSET
1,2
FORMULA
a(n) = 2a(n-4) for n > 7. - Charles R Greathouse IV, Feb 18 2013
G.f.: -x*(x+1)^2*(x^2+1)^2 / (2*x^4-1). - Colin Barker, Jul 19 2013
Sum_{n>=1} 1/a(n) = 352/105. - Amiram Eldar, Feb 18 2021
MATHEMATICA
CoefficientList[Series[-(x + 1)^2 (x^2 + 1)^2/(2 x^4 - 1), {x, 0, 50}], x] (* Vincenzo Librandi, Oct 19 2013 *)
LinearRecurrence[{0, 0, 0, 2}, {1, 2, 3, 4, 5, 6, 7}, 50] (* Harvey P. Dale, Aug 24 2019 *)
PROG
(PARI) a(n)=if(n<9, n, [4, 5, 6, 7][n%4+1]<<(n\4-1)) \\ Charles R Greathouse IV, Feb 18 2013
CROSSREFS
Sequence in context: A060471 A003045 A279079 * A266480 A246080 A278619
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms from Colin Barker, Jul 19 2013
STATUS
approved