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A224930 Numbers n such that n divides the concatenation of all divisors in descending order. 8
1, 561, 1703, 2883, 11623, 14721, 32431, 205119, 361767, 826471901, 3747204067, 17463443163, 404345080971, 573488405493, 5623233497397 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Like A069872 but in descending order.
a(11) > 2*10^9. - Donovan Johnson, May 05 2013
a(16) > 10^13. - Giovanni Resta, Feb 14 2020
LINKS
EXAMPLE
Divisors of 561 are 1, 3, 11, 17, 33, 51, 187, 561 and 5611875133171131 / 561 = 10003342483371.
Divisors of 1703 are 1, 13, 131, 1703 and 1703131131 / 1703 = 1000077.
MAPLE
with(numtheory); A224930:=proc(q) local a, b, c, d, f, k, n;
for n from 1 to q do a:=sort([op(divisors(n))]); b:=nops(a); c:=a[b];
for k from 1 to b-1 do d:=c; f:=0; while d>0 do f:=f+1; d:=trunc(d/10); od;
c:=c+a[k+1]*10^f; od; if type(c/n, integer) then print(n); fi;
od; end: A224930 (10^6); # Paolo P. Lava, May 02 2013
MATHEMATICA
Select[Range[10^6/2]*2-1, Mod[ FromDigits@ Flatten@ IntegerDigits[ Reverse@ Divisors@ #], #] == 0 &] (* Giovanni Resta, May 05 2013 *)
PROG
(PARI) isok(k) = {my(s = "", d = Vecrev(divisors(k))); for (j=1, #d, s = concat(s, Str(d[j])); ); eval(k) % k == 0; } \\ Michel Marcus, Feb 14 2020
CROSSREFS
Cf. A069872.
Sequence in context: A131672 A321156 A227976 * A083732 A292367 A290805
KEYWORD
nonn,base,more
AUTHOR
Paolo P. Lava, May 02 2013
EXTENSIONS
a(10) from Donovan Johnson, May 05 2013
a(11)-a(12) from Giovanni Resta, May 05 2013
a(13)-a(14) from Giovanni Resta, May 10 2013
a(15) from Giovanni Resta, Feb 14 2020
STATUS
approved

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Last modified March 28 11:44 EDT 2024. Contains 371241 sequences. (Running on oeis4.)