cp's OEIS Frontend

A118252 The least positive integer whose reversed binary representation does not occur in the concatenation of the reversed binary representations of all preceding terms.

%I A118252 #20 Aug 12 2023 05:13:32
%S A118252 1,2,3,4,8,10,11,12,15,16,22,24,27,32,35,36,38,43,44,54,59,64,66,70,
%T A118252 76,79,83,85,88,91,95,97,99,116,122,127,128,130,132,136,140,147,148,
%U A118252 150,155,158,163,169,170,175,176,179,182,184,192,196,201,217,232
%N A118252 The least positive integer whose reversed binary representation does not occur in the concatenation of the reversed binary representations of all preceding terms.
%C A118252 See the variant A118250 for comments and examples.
%H A118252 Michael De Vlieger, <a href="/A118252/b118252.txt">Table of n, a(n) for n = 1..10000</a>
%t A118252 a = {1}; b = {1}; Do[k = b[[i - 1]] + 1; While[SequenceCount[Flatten@ a, Set[d, Reverse@ IntegerDigits[k, 2]]] != 0, k++]; a = Join[a, d]; AppendTo[b, k], {i, 2, 59}]; b (* _Michael De Vlieger_, Aug 21 2017 *)
%o A118252 (PARI) A118252(n,show=0,a=1)={my(c=[a],S=[],L); for(k=1,n, show & print1(a","); while( setsearch(S,binary(a++)),); c=concat(binary(a),c); S=[]; for(i=0,#c-L=#binary(a), c[i+1] & for(j=i+L,min(i+L+1,#c), S=setunion(S,Set(t=[vecextract(c,2^j-2^i)])))));a}  \\ _M. F. Hasler_, Dec 29 2012
%Y A118252 Cf. A118248 (variant without reversal), A118250 (the same with a(0)=0), A118251 (concatenation of terms in binary).
%Y A118252 Cf. A190896.
%K A118252 easy,nonn
%O A118252 1,2
%A A118252 _Leroy Quet_, Apr 18 2006
%E A118252 More terms from _Graeme McRae_, Apr 19 2006
%E A118252 Explicit definition from _M. F. Hasler_, Dec 29 2012