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A175880 a(1)=1, a(2)=2. If n >= 3: if n/2 is in the sequence, a(n)=0, otherwise a(n)=n.

%I A175880 #21 May 12 2019 02:18:19
%S A175880 1,2,3,0,5,0,7,8,9,0,11,12,13,0,15,0,17,0,19,20,21,0,23,0,25,0,27,28,
%T A175880 29,0,31,32,33,0,35,36,37,0,39,0,41,0,43,44,45,0,47,48,49,0,51,52,53,
%U A175880 0,55,0,57,0,59,60,61,0,63,0,65,0,67,68,69,0,71,0,73,0,75,76,77,0,79,80
%N A175880 a(1)=1, a(2)=2. If n >= 3: if n/2 is in the sequence, a(n)=0, otherwise a(n)=n.
%C A175880 If n > 0 and n is in the sequence, then a(2*n) = 0. Example: 5 is in the sequence, so a(2*5) = a(10) = 0.
%C A175880 Is this a(n) = n*A039982(n-1), n > 1? [_R. J. Mathar_, Dec 07 2010]
%H A175880 Reinhard Zumkeller, <a href="/A175880/b175880.txt">Table of n, a(n) for n = 1..10000</a>
%F A175880 a(n) = n - (1 + (-1)^n) * a((2*n + 1 - (-1)^n)/4), n >= 3.
%F A175880 a(n) = n - A010673(n+1)*a(A110654(n)).
%p A175880 A110654 := proc(n) 2*n+1-(-1)^n ; %/4 ;end proc:
%p A175880 A175880 := proc(n) if n <=2 then n; else if type(n,'even') then n-2*procname(A110654(n)) ; else n; end if; end if; end proc:
%p A175880 seq(A175880(n),n=1..40) ; # _R. J. Mathar_, Dec 07 2010
%o A175880 (Haskell)
%o A175880 import Data.List (delete)
%o A175880 a175880 n = a175880_list !! (n-1)
%o A175880 a175880_list = 1 : f [2..] [2..] where
%o A175880    f (x:xs) (y:ys) | x == y    = x : (f xs $ delete (2*x) ys)
%o A175880                    | otherwise = 0 : (f xs (y:ys))
%o A175880 for_bFile = take 10000 a175880_list
%o A175880 -- _Reinhard Zumkeller_, Feb 09 2011
%Y A175880 Cf. A053661.
%Y A175880 A000040, A001749, A002001, A002042, A002063, A002089, A003947, A004171 and A081294 are subsequences.
%K A175880 easy,nonn
%O A175880 1,2
%A A175880 _Adriano Caroli_, Dec 05 2010