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%I A099004 #17 May 13 2019 20:57:33
%S A099004 1,2,3,-4,5,6,-9,7,8,-14,10,11,-18,12,13,-24,15,16,-30,17,19,-34,20,
%T A099004 21,-39,22,23,-43,25,26,-50,27,28,-54,29,31,-57,33,-32,35,36,-70,37,
%U A099004 38,-73,40,41,-78,42,44,-85,45,46,-90,47,48,-94,49,51,-97,52,53,-104,55,56,-109,58,59,-116,61,-60,62,63
%N A099004 First differences of A081145.
%C A099004 Does every number appear in the sequence of absolute values (see A308007)?
%H A099004 Chai Wah Wu, <a href="/A099004/b099004.txt">Table of n, a(n) for n = 1..5000</a>
%t A099004 f[s_] := Block[{k = 1, d = Abs[Most@s - Rest@s], l = Last@s}, While[MemberQ[s, k] || MemberQ[d, Abs[l - k]], k++ ]; Append[s, k]]; t = Nest[f, {1}, 75]; Rest@t - Most@t (* _Robert G. Wilson v_, Jun 13 2006 *)
%o A099004 (Python)
%o A099004 A099004_list, l, s, b1, b2 = [1], 2, 3, set(), set([1])
%o A099004 for n in range(2, 5*10**3+1):
%o A099004 ....i = s
%o A099004 ....while True:
%o A099004 ........m = abs(i-l)
%o A099004 ........if not (i in b1 or m in b2):
%o A099004 ............A099004_list.append(i-l)
%o A099004 ............b1.add(i)
%o A099004 ............b2.add(m)
%o A099004 ............l = i
%o A099004 ............while s in b1:
%o A099004 ................b1.remove(s)
%o A099004 ................s += 1
%o A099004 ............break
%o A099004 ........i += 1 # _Chai Wah Wu_, Dec 15 2014
%Y A099004 Cf. A081145, A081146, A308007, A308021.
%K A099004 sign,easy
%O A099004 1,2
%A A099004 _Amarnath Murthy_ and Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jun 17 2003
%E A099004 Edited by _N. J. A. Sloane_, Apr 08 2006
%E A099004 More terms from _Robert G. Wilson v_, Jun 13 2006

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