Search: id:A005940
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%I A005940 M0509
%S A005940 1,2,3,4,5,6,9,8,7,10,15,12,25,18,27,16,11,14,21,20,35,30,45,24,49,50,
%T A005940 75,36,125,54,81,32,13,22,33,28,55,42,63,40,77,70,105,60,175,90,135,48,
%U A005940 121,98,147,100,245,150,225,72,343,250,375,108,625,162,243,64,17,26,39
%N A005940 The Doudna sequence: write n-1 in binary; power of p_k in a(n) is # of 
               1's that are followed by k-1 0's.
%C A005940 A permutation of the natural numbers. - Robert G. Wilson v (rgwv(AT)rgwv.com), 
               Feb 22 2005
%C A005940 Fixed points: A029747. - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), 
               Aug 23 2006
%D A005940 R. E. Kutz, Two unusual sequences, Two-Year College Mathematics Journal, 
               12 (1981), 316-319.
%D A005940 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A005940 R. Zumkeller, <a href="b005940.txt">Table = of n, a(n) for n = 1..1024</
               a>
%H A005940 <a href="Sindx_Per.html#IntegerPermutation">Index entries for sequences 
               that are permutations of the natural numbers</a>
%F A005940 a(n) = f(n-1, 1, 1) with f(n, i, x) = if n=0 then x = else (if n mod 
               2 = 0 then f(n/2, i+1, x) else f((n+1)/2, i, x*prime(i))). - Reinhard 
               Zumkeller (reinhard.zumkeller(AT)gmail.com), Aug 23 2006
%t A005940 f[n_] := Block[{p = Partition[ Split[ Join[ IntegerDigits[n - 1, 2], 
               {2}]], 2]}, Times @@ Flatten[ Table[q = Take[p, -i]; Prime[ Count[ 
               Flatten[q], 0] + 1]^q[[1, 1]], {i, Length[p]}] ]]; Table[ f[n], {n, 
               67}] (from Robert G. Wilson v Feb 22 2005)
%Y A005940 Cf. A103969. Inverse is A005941.
%Y A005940 Sequence in context: A099004 A055170 A068384 this_sequence A005941 A075164 
               A023841
%Y A005940 Adjacent sequences: A005937 A005938 A005939 this_sequence A005941 A005942 
               A005943
%K A005940 nonn,easy,nice
%O A005940 1,2
%A A005940 N. J. A. Sloane (njas(AT)research.att.com) and J. H. Conway (conway(AT)math.princeton.edu)
%E A005940 More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Feb 22 2005

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