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A147675
Divide by 2, multiply by 4, repeat.
4
10, 5, 20, 10, 40, 20, 80, 40, 160, 80, 320, 160, 640, 320, 1280, 640, 2560, 1280, 5120, 2560, 10240, 5120, 20480, 10240, 40960, 20480, 81920, 40960, 163840, 81920, 327680, 163840, 655360, 327680, 1310720, 655360, 2621440, 1310720, 5242880
OFFSET
1,1
COMMENTS
A147675-A147678 are from a quiz that someone asked me to help them with.
FORMULA
From R. J. Mathar, Apr 22 2009: (Start)
a(n) = 2*a(n-2) = 5*A135530(n-1).
G.f.: 5*x*(2+x)/(1-2*x^2). (End)
From Amiram Eldar, Feb 02 2024: (Start)
Sum_{n>=1} 1/a(n) = 3/5.
Sum_{n>=1} (-1)^n/a(n) = 1/5. (End)
MATHEMATICA
LinearRecurrence[{0, 2}, {10, 5}, 50] (* Paolo Xausa, Jan 30 2024 *)
CROSSREFS
Sequence in context: A280154 A040093 A046797 * A070291 A361671 A183132
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Apr 21 2009
EXTENSIONS
More terms from R. J. Mathar, Apr 22 2009
STATUS
approved