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A223078 Positive integers with the property that if the base-4 representation is reversed the result is three times the original number. 2
75, 315, 1275, 5115, 19275, 20475, 76875, 81915, 307275, 322875, 327675, 1228875, 1290555, 1310715, 4915275, 4934475, 5161275, 5223675, 5242875, 19660875, 19741515, 20644155, 20890875, 20971515, 78643275, 78720075, 78969675, 82575675, 82652475, 83559675 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

From Robert Israel, Apr 23 2019: (Start)

All terms are divisible by 15.

If x is a term and x < 4^k, then x*(4^k+1) is a term.  In particular the sequence is infinite. (End)

LINKS

Robert Israel, Table of n, a(n) for n = 1..985

MAPLE

rev4:= proc(n) local L, i;

  L:= convert(n, base, 4);

  add(L[-i]*4^(i-1), i=1..nops(L))

end proc:

Res:= NULL:

for d from 2 to 15 do

  d1:= ceil(d/2); d2:= d-d1;

  for a from 4^(d1-1) to 4^d1/3 do

     b:= rev4(a)/3 mod 4^d2;

     x:= 4^d2*a+b;

     if rev4(x) = 3*x then Res:= Res, x; fi

od od:

Res; # Robert Israel, Apr 23 2019

MATHEMATICA

Select[Range[84*10^6], 3#==FromDigits[Reverse[IntegerDigits[#, 4]], 4]&] (* Harvey P. Dale, Mar 03 2018 *)

CROSSREFS

Cf. A173951, A223077, A223079, A214927.

Sequence in context: A292313 A158765 A226741 * A055561 A193252 A223452

Adjacent sequences:  A223075 A223076 A223077 * A223079 A223080 A223081

KEYWORD

nonn,base

AUTHOR

N. J. A. Sloane, Mar 14 2013

EXTENSIONS

More terms from Alois P. Heinz, Mar 14 2013

STATUS

approved

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Last modified December 15 00:30 EST 2019. Contains 329988 sequences. (Running on oeis4.)