A045135 Numbers whose base-4 representation contains no 2's and exactly two 3's.

15, 31, 51, 55, 60, 61, 79, 95, 115, 119, 124, 125, 195, 199, 204, 205, 211, 215, 220, 221, 240, 241, 244, 245, 271, 287, 307, 311, 316, 317, 335, 351, 371, 375, 380, 381, 451, 455, 460, 461, 467, 471, 476, 477, 496, 497, 500

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

f:= proc(d) # for terms < 4^d
local L, x1, x2, i, S, R;
   R:= NULL;
   for x2 from 1 to d-1 do
     for x1 from 0 to x2-1 do
       for S in combinat:-powerset({$0..x1-1, $x1+1..x2-1, $x2+1..d-1}) do
         R:= R, add(4^i, i=S)+3*4^x1+3*4^x2;
   od od od:
   sort([R]);
end proc:
f(5); # Robert Israel, Feb 25 2021

Mathematica

Select[Range[500], DigitCount[#, 4, 2]==0&&DigitCount[#, 4, 3]==2&] (* Harvey P. Dale, Jul 24 2016 *)

Prog

(PARI) isok(k) = my(d=digits(k, 4)); (#select(x->(x==2), d) == 0) && (#select(x->(x==3), d) == 2); \\ Michel Marcus, Feb 25 2021

Crossrefs

Cf. A007090 (numbers in base 4).

Sequence in context: A044457 A249452 A132757 * A283122 A195046 A324631

Adjacent sequences: A045132 A045133 A045134 * A045136 A045137 A045138

Keyword

nonn,base

Author

Clark Kimberling

Status

approved