A043885 - OEIS

%I #22 Sep 04 2023 12:33:51

%S 11,14,27,30,47,59,62,75,78,91,94,111,123,126,139,142,155,158,191,203,

%T 206,219,222,239,251,254,267,270,283,286,303,315,318,331,334,347,350,

%U 367,379,382,395,398,411,414,447,459,462,475,478,495,507,510,523,526,539,542

%N Numbers k such that 2 and 3 occur juxtaposed in the base-4 representation of k but not of k+1.

%H David A. Corneth, <a href="/A043885/b043885.txt">Table of n, a(n) for n = 1..10000</a>

%e 27 is in the sequence as 27_10 = 123_4 which has 23 juxtaposed in its base-4 representationand 28_10 = 130_4 does not have 23 juxtaposed in its base-4 representation. - _David A. Corneth_, Aug 28 2023

%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,4],{2,3}]>0 || SequenceCount[ IntegerDigits[ n,4],{3,2}]>0,1,0],{n,500}],{1,0}][[;;,1]] (* _Harvey P. Dale_, Aug 28 2023 *)

%o (PARI) is(n) = {has23juxtaposed(n) && !has23juxtaposed(n+1)}

%o has23juxtaposed(n) = {my(d = digits(n, 4)); for(i = 1, #d-1, if(d[i] == 2 && d[i+1] == 3, return(1)); if(d[i] == 3 && d[i+1] == 2, return(1))); 0} \\ _David A. Corneth_, Aug 28 2023

%Y Cf. A007090.

%Y Cf. A043880, A043881, A043882, A043883, A043884.

%K nonn,base

%O 1,1

%A _Clark Kimberling_

%E More terms from _David A. Corneth_, Aug 28 2023