cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A293427 Squarefree numbers such that there are no adjacent 0's in their binary expansions.

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%I A293427 #11 Oct 13 2017 06:03:58
%S A293427 1,2,3,5,6,7,10,11,13,14,15,21,22,23,26,29,30,31,42,43,46,47,53,55,58,
%T A293427 59,61,62,85,86,87,91,93,94,95,106,107,109,110,111,118,119,122,123,
%U A293427 127,170,173,174,181,182,183,186,187,190,191,213,214,215,218,219,221,222,223,235,237,238,239,246,247,251,253,254,255,341
%N A293427 Squarefree numbers such that there are no adjacent 0's in their binary expansions.
%H A293427 Antti Karttunen, <a href="/A293427/b293427.txt">Table of n, a(n) for n = 1..10000</a>
%H A293427 <a href="/index/Bi#binary">Index entries for sequences related to binary expansion of n</a>
%e A293427 55 is present as 55 = 5*11 is squarefree (in A005117) and A007088(55) = 110111 does not contain two adjacent 0's. However, it is not present in A293430 because floor(55/2) = 27 is not a squarefree number.
%t A293427 Select[Range@ 360, And[SquareFreeQ@ #, SequenceCount[IntegerDigits[#, 2], {0, 0}] == 0] &] (* _Michael De Vlieger_, Oct 11 2017 *)
%o A293427 (PARI)
%o A293427 isA003754(n) = { n=bitor(n, n>>1)+1; n>>=valuation(n, 2); (n==1); }; \\ After _Charles R Greathouse IV_'s Feb 06 2017 code.
%o A293427 n=1; k=1; while(k <= 10000, if(isA003754(n)&&issquarefree(n),write("b293427.txt", k, " ", n);k=k+1); n=n+1;); \\ _Antti Karttunen_, Oct 11 2017
%Y A293427 Intersection of A003754 and A005117.
%Y A293427 A293430 is a subsequence from which this differs for the first time at n=24, where a(24) = 55, a term not present in A293430.
%K A293427 nonn,base
%O A293427 1,2
%A A293427 _Antti Karttunen_, Oct 11 2017