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A061808 a(n) is the smallest number with all digits odd that is divisible by 2n-1. 3
1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 315, 115, 75, 135, 319, 31, 33, 35, 37, 39, 533, 559, 135, 517, 539, 51, 53, 55, 57, 59, 793, 315, 195, 335, 759, 71, 73, 75, 77, 79, 1377, 913, 595, 957, 979, 91, 93, 95, 97, 99, 1111, 515, 315, 535, 1199, 111, 113, 115, 117 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

From Yang Haoran, Dec 02 2017: (Start)

Record value for a(n) = (2n-1) * A296009(n).

   (1, 3, 5, ..., 19) * 1 = (1, 3, 5, ..., 19)

   21 *  15 =    315

   29 *  11 =    319

   41 *  13 =    533

   43 *  13 =    559

   61 *  13 =    793

   81 *  17 =   1377

  127 *  11 =   1397

  129 *  15 =   1935

  149 *  13 =   1937

  167 *  19 =   3173

  169 *  33 =   5577

  201 * 155 =  31155

  299 * 105 =  31395

  401 * 133 =  53333

  601 * 119 =  71519

  633 * 283 = 179139

(the list above is complete)

...

990001 * 12121113 = 11999913991113 (the first A296009(n) > 2n-1).

(End)

LINKS

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

Mathematical Excalibur, Problem 300, Vol. 1 No. 3 p. 3, 2008.

MAPLE

Ad[1]:= [1, 3, 5, 7, 9]:

for n from 2 to 9 do Ad[n]:= map(t -> seq(10*t+j, j=[1, 3, 5, 7, 9]), Ad[n-1]) od:

Aod:= [seq(op(Ad[i]), i=1..9)]:

f:= proc(n) local k;

   for k from 1 to nops(Aod) do

       if Aod[k] mod (2*n-1) = 0 then return(Aod[k]) fi

     od;

     NotFound

end proc:

map(f, [$1..100]); # Robert Israel, Feb 15 2017

MATHEMATICA

Table[Block[{k = 2 n - 1}, While[Nand[AllTrue[IntegerDigits@ k, OddQ], Divisible[k, 2 n - 1]], k += 2]; k], {n, 59}] (* Michael De Vlieger, Dec 02 2017 *)

PROG

(MAGMA) a:=[]; for n in [1..120 by 2] do k:=1; while not Set(Intseq(n*k)) subset {1, 3, 5, 7, 9} do k:=k+2; end while; Append(~a, k*n); end for; a; // Marius A. Burtea, Sep 20 2019

(PARI) isoddd(n) = #select(x->((x%2) == 0), digits(n)) == 0;

a(n) = {my(m = 2*n-1, k = 1); while(!isoddd(k*m), k++); k*m; } \\ Michel Marcus, Sep 20 2019

CROSSREFS

Cf. A061807, A014261.

Equals A296009 * (2n-1).

Sequence in context: A014261 A066640 A137507 * A248608 A309325 A192863

Adjacent sequences:  A061805 A061806 A061807 * A061809 A061810 A061811

KEYWORD

base,nonn,look

AUTHOR

Amarnath Murthy, May 28 2001

EXTENSIONS

Corrected and extended by Larry Reeves (larryr(AT)acm.org), May 30 2001

STATUS

approved

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Last modified December 8 02:41 EST 2021. Contains 349590 sequences. (Running on oeis4.)