This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a(19) = 19 because the digits are already in increasing order. a(20) = 2 because the digits of 20 are 2 and 0, which in increasing order are 0 and 2, but since zero-padding is not allowed on the left, the zero digit is dropped and we are left with 2. a(21) = 12 because the digits of 21 are 2 and 1, which in increasing order are 1 and 2.
import Data.List (sort) a004185 n = read $ sort $ show n :: Integer -- Reinhard Zumkeller, Aug 10 2011
A004185:=func; [n eq 0 select 0 else A004185(n): n in [0..57]]; // Bruno Berselli, Apr 03 2012
A004185 := proc(n) local dgs; convert(n,base,10) ; dgs := sort(%,`>`) ; add( op(i,dgs)*10^(i-1),i=1..nops(dgs)) ; end proc: seq(A004185(n),n=0..20) ; # R. J. Mathar, Jul 26 2015
FromDigits[Sort[DeleteCases[IntegerDigits[#], 0]]]&/@Range[0, 60] (* Harvey P. Dale, Nov 29 2011 *)
a(n)=fromdigits(vecsort(digits(n))) \\ Charles R Greathouse IV, Feb 06 2017
def A004185(n): return int(''.join(sorted(str(n))).replace('0','')) if n > 0 else 0 # Chai Wah Wu, Nov 10 2015
a193581 n = n - a004185 n a193581_list = map a193581 [0..]
ss[n_]:=n-FromDigits[Sort[Select[IntegerDigits[n],#>0&]]]; Array[ss,80,0] (* Harvey P. Dale, Aug 13 2013 *)
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