cp's OEIS Frontend

A081926 Triangle read by rows in which n-th row gives n smallest numbers with digit sum n.

%I A081926 #19 Feb 20 2018 07:39:12
%S A081926 1,2,11,3,12,21,4,13,22,31,5,14,23,32,41,6,15,24,33,42,51,7,16,25,34,
%T A081926 43,52,61,8,17,26,35,44,53,62,71,9,18,27,36,45,54,63,72,81,19,28,37,
%U A081926 46,55,64,73,82,91,109,29,38,47,56,65,74,83,92,119,128,137
%N A081926 Triangle read by rows in which n-th row gives n smallest numbers with digit sum n.
%H A081926 Robert Israel, <a href="/A081926/b081926.txt">Table of n, a(n) for n = 1..10011</a> (first 141 rows, flattened; first 40 rows from T. D. Noe)
%e A081926 Triangle starts
%e A081926 1
%e A081926 2 11
%e A081926 3 12 21
%e A081926 4 13 22 31
%e A081926 5 14 23 32 41
%p A081926 f:= proc(n) local Res, d, v, count;
%p A081926     Res:= NULL; count:= 0;
%p A081926     for d from ceil(n/9) while count < n do
%p A081926        v:= g(n,d,n-count,1);
%p A081926        Res:= Res, op(v);
%p A081926        count:= count + nops(v);
%p A081926     od:
%p A081926     Res
%p A081926 end proc:
%p A081926 g:= proc(n,d,remain) local rem, Res, j, j0, v;
%p A081926       if remain = 0 then return [] else rem:= remain fi;
%p A081926       if nargs = 4 then j0:= 1 else j0:= 0 fi;
%p A081926       if d = 1 then if n >= j0 and n <= 9 then [n] else [] fi
%p A081926       else
%p A081926         Res:= NULL;
%p A081926         for j from max(j0, ceil(n-9*(d-1))) to min(9,n) while rem > 0 do
%p A081926           v:= map(t -> j*10^(d-1)+t, procname(n-j,d-1,rem));
%p A081926           Res:= Res, op(v);
%p A081926           rem:= rem - nops(v);
%p A081926         od;
%p A081926         [Res]
%p A081926       fi
%p A081926 end proc:
%p A081926 for i from 1 to 25 do f(i) od; # _Robert Israel_, Feb 19 2018
%t A081926 Needs["Combinatorica`"]; Table[Take[Union[Flatten[Table[FromDigits /@ Permutations[PadRight[s, 6]], {s, Partitions[n, 9]}]]], n], {n, 40}] (* _T. D. Noe_, Mar 08 2013 *)
%Y A081926 Cf. A081927, A081928.
%K A081926 base,easy,nonn,tabl,look
%O A081926 1,2
%A A081926 _Amarnath Murthy_, Apr 01 2003