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A167232 a(n) is the number obtained by writing out numbers from 1 to n and placing an alternate + and - minus sign between successive digits and evaluating the expression written. 2

%I

%S 1,-1,2,-2,3,-3,4,-4,5,4,4,3,4,3,5,4,7,6,10,9,14,13,19,18,25,24,32,31,

%T 40,38,38,36,37,35,37,35,38,36,40,38,43,41,47,45,52,50,58,56,65,62,62,

%U 59,60,57,59,56,59,56,60,57,62,59,65,62,69,66,74,71,80,76,76,72,73,69

%N a(n) is the number obtained by writing out numbers from 1 to n and placing an alternate + and - minus sign between successive digits and evaluating the expression written.

%H Sphere Online Judge, <a href="http://www.spoj.pl/problems/KPSUM/">Problem 1433: The Sum</a> [Link edited by _N. J. A. Sloane_, Nov 02 2009]

%F a(n) = -sum_{i=1..n} (-1)^i*A007376(i). [From _R. J. Mathar_, Nov 09 2009]

%K sign,base

%O 1,3

%A Dhruv (dhruvbird(AT)gmail.com), Oct 31 2009

%E a(12) corrected, more terms appended by _R. J. Mathar_, Nov 09 2009

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Last modified January 24 15:43 EST 2022. Contains 350540 sequences. (Running on oeis4.)