%I
%S 1,0,1,2,3,4,5,6,7,8,2,1,0,1,2,3,4,5,6,7,3,2,1,0,1,2,3,4,5,6,4,3,2,1,
%T 0,1,2,3,4,5,5,4,3,2,1,0,1,2,3,4,6,5,4,3,2,1,0,1,2,3,7,6,5,4,3,2,1,0,
%U 1,2,8,7,6,5,4,3,2,1,0,1,9,8,7,6,5,4,3,2,1,0,10,11,12,13,14,15,16,17,18,19,1
%N Concatenate absolute values of differences between adjacent digits of n.
%C Let the decimal expansion of n be abcd...efg, say. Then a(n) has decimal expansion ab bc cd ... ef fg. Leading zeros in a(n) are omitted.
%C From _M. F. Hasler_, Nov 09 2019: (Start)
%C This sequence coincides with A080465 up to a(109) but is thereafter completely different.
%C It would make sense to define a(n) = 0 for n = 0, ..., 9.
%C Eric Angelini calls a(n) the "ghost" of the number n and considers iterations of n > n + a(n) depending on parity of a(n), cf. A329200 and A329201. (End)
%H T. D. Noe, <a href="/A040115/b040115.txt">Table of n, a(n) for n = 10..10000</a>
%H E. Angelini, <a href="http://cinquantesignes.blogspot.com/2019/11/theghostiteration.html">The Ghost Iteration</a>, Personal blog "Cinquante signes", Nov 2019
%e a(371) = 46, for example.
%e a(110) = 01 = 1, while A080465(110) = 10  1 = 9.  _M. F. Hasler_, Nov 09 2019
%o (PARI) apply( A040115(n)=fromdigits(abs((n=digits(n+!n))[^1]n[^1])), [10..199]) \\ Works for all n >= 0.  _M. F. Hasler_, Nov 09 2019
%Y Cf. A037904, A040114, A040163, A040997.
%Y Cf. A329200, A329201: iterations of n + a(n).
%K nonn,base,easy
%O 10,4
%A _Felice Russo_
%E Definition clarified by _N. J. A. Sloane_, Aug 19 2008
%E Name edited by _M. F. Hasler_, Nov 09 2019
