A043885 Numbers k such that 2 and 3 occur juxtaposed in the base-4 representation of k but not of k+1.

11, 14, 27, 30, 47, 59, 62, 75, 78, 91, 94, 111, 123, 126, 139, 142, 155, 158, 191, 203, 206, 219, 222, 239, 251, 254, 267, 270, 283, 286, 303, 315, 318, 331, 334, 347, 350, 367, 379, 382, 395, 398, 411, 414, 447, 459, 462, 475, 478, 495, 507, 510, 523, 526, 539, 542

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• base

Examples

			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
		

Links

• David A. Corneth, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A007090.

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

Programs

Mathematica

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 *)

PARI

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

Extensions

More terms from David A. Corneth, Aug 28 2023