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a(1) = 11. a(n) is obtained by filling the space between neighboring digits in a(n-1) with their sum.
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%I #11 Apr 24 2023 14:18:04

%S 11,121,13231,143525341,15473857275837451,

%T 1659411710311813512792971251381131071149561,

%U 176115149134512187811033412198914385613297169112119167813275614311891214341107781215413914511671

%N a(1) = 11. a(n) is obtained by filling the space between neighboring digits in a(n-1) with their sum.

%C If we consider a(1) = 11 to be a binary number and recursively construct a(n) by filling the space between neighboring bits in a(n-1) with their binary sum we obtain the binary sequence 11, 1101, 11011011, 110110111011011011101, .... This sequence converges to the Sturmian word A080764. - _Peter Bala_, Jan 30 2015

%e a(2) = 121; for a(3), in 1-2-1 the two (-) are replaced by 1+2 = 3 hence a(3)=13231.

%Y Cf. A080764, A216208.

%K base,easy,nonn

%O 1,1

%A _Amarnath Murthy_, Jul 29 2005

%E More terms from Maire O'Neill (mbo5001(AT)psu.edu), Oct 04 2005