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%I #24 Aug 12 2023 13:44:15
%S 0,6,42,48,294,300,336,342,2058,2064,2100,2106,2352,2358,2394,2400,
%T 14406,14412,14448,14454,14700,14706,14742,14748,16464,16470,16506,
%U 16512,16758,16764,16800,16806,100842,100848,100884,100890,101136
%N Numbers whose set of base 7 digits is {0,6}.
%C n such that there exists a permutation p_1, ..., p_n of 1, ..., n such that i + p_i is a power of 7 for every i.
%H Vincenzo Librandi, <a href="/A097253/b097253.txt">Table of n, a(n) for n = 1..200</a>
%F a(n) = 6*A033044(n).
%F a(2n) = 7*a(n), a(2n+1) = a(2n)+6.
%t fQ[n_]:=Union@Join[{0,6},IntegerDigits[n,7]]=={0,6};Select[Range[0,140000],fQ] (* _Vincenzo Librandi_, May 25 2012 *)
%t FromDigits[#,7]&/@Tuples[{0,6},6] (* This program is several thousand times faster than the first program, above. *) (* _Harvey P. Dale_, Aug 12 2023 *)
%o (Magma) [n: n in [0..200000] | Set(IntegerToSequence(n, 7)) subset {0, 6}]; // _Vincenzo Librandi_, May 25 2012
%o (Maxima) a[0]:0$ a[n]:=7*a[floor(n/2)]+3*(1-(-1)^n)$ makelist(a[n], n, 0, 36); /* _Bruno Berselli_, May 25 2012 */
%Y Cf. A001196, A005823, A097251-A097262.
%K nonn,base
%O 1,2
%A _Ray Chandler_, Aug 03 2004
%E Offset corrected by _Arkadiusz Wesolowski_, Nov 09 2013