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A045135 Numbers whose base-4 representation contains no 2's and exactly two 3's. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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
KEYWORD
nonn,base
AUTHOR
STATUS
approved

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Last modified April 21 04:17 EDT 2024. Contains 371850 sequences. (Running on oeis4.)