A044973 Numbers whose base-3 representation contains exactly one 0 and three 1's.

31, 37, 39, 95, 97, 103, 113, 115, 119, 123, 127, 129, 139, 145, 147, 175, 193, 199, 201, 287, 293, 295, 311, 313, 319, 341, 347, 349, 359, 371, 375, 383, 385, 389, 393, 397, 399, 419, 421, 427, 437, 439, 443, 447, 451, 453, 463

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• base
• look

Examples

			31 = 1011_3; 37 = 1101_3; 39 = 1110_3; 95 = 10112_3.
		

Links

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

Crossrefs

Cf. A007089 (numbers in base 3), A044971 (1 zero 1 one), A044972 (1 zero 2 ones), A044974 (1 zero 4 ones).

Programs

Maple

f:= proc(d) local x,R,i,j,j3;
  x:= 3^d-1;
  op(sort([seq(seq(x - add(3^j, j = j3) - 2*3^i, i= {$0..d-2} minus j3) , j3 =combinat:-choose({$0..d-1},3))]))
end proc:
map(f, [$4..6]); # Robert Israel, Apr 20 2021

Mathematica

Select[Range[500],DigitCount[#,3,0]==1&&DigitCount[#,3,1]==3&] (* Harvey P. Dale, Jul 12 2019 *)

PARI

isok(k) = my(d=digits(k,3)); (#select(x->(x==0), d) == 1) && (#select(x->(x==1), d) == 3); \\ Michel Marcus, Apr 21 2021