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%I #18 Jun 20 2017 12:24:30
%S 1,-2,3,-4,5,-6,7,-8,9,10,11,8,13,6,15,4,17,2,19,-20,-19,-22,-17,-24,
%T -15,-26,-13,-28,-11,30,31,28,33,26,35,24,37,22,39,-40,-39,-42,-37,
%U -44,-35,-46,-33,-48,-31,50,51,48,53,46,55,44,57,42,59,-60,-59,-62,-57,-64,-55,-66,-53,-68,-51,70,71,68,73,66,75,64,77,62
%N In decimal number system, take even digits of n with negative sign.
%C See A121758. In decimal number system, take odd digits of n with negative sign.
%C a(A014261(n)) = A014261(n). - _Reinhard Zumkeller_, Nov 30 2007
%H Reinhard Zumkeller, <a href="/A121759/b121759.txt">Table of n, a(n) for n = 1..10000</a>
%F If n = d(i)*10^(i-1), then a(n) = (-1)^(1+d(i))*d(i)*10^(i-1).
%F a(n) = -A121758(n).
%e a(12) = 8 because 12 = 1*10^1 + 2*10^0 and a(12) = (-1)^(1+1)*1*10^1 + (-1)^(1+2)*2*10^0 = 10-2 = 8.
%t a[n_] := Total[MapIndexed[(-1)^(#1 + 1)*#1*10^(#2[[1]] - 1)&, Reverse[ IntegerDigits[n]]]]; Array[a, 78] (* _Jean-François Alcover_, Jun 20 2017 *)
%o (Haskell)
%o import Data.List (unfoldr)
%o a121759 = foldl f 0 . reverse . unfoldr d where
%o d 0 = Nothing
%o d x = Just $ swap $ divMod x 10
%o f v d | even d = 10 * v - d
%o | odd d = 10 * v + d
%o -- _Reinhard Zumkeller_, Aug 01 2011
%Y Cf. A121758.
%K base,sign,nice,look
%O 1,2
%A _Zak Seidov_, Aug 20 2006
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