A244112 - OEIS

%I #22 Feb 25 2018 02:01:39

%S 10,11,12,13,14,15,16,17,18,19,1110,21,1211,1311,1411,1511,1611,1711,

%T 1811,1911,1210,1211,22,1312,1412,1512,1612,1712,1812,1912,1310,1311,

%U 1312,23,1413,1513,1613,1713,1813,1913,1410,1411,1412,1413,24,1514,1614,1714

%N Reverse digit count of n in decimal representation.

%C Frequencies of digits 0 through 9, occurring in n, are summarized in order of decreasing digits;

%C a(A010785(n)) = A047842(A010785(n)).

%H Reinhard Zumkeller, <a href="/A244112/b244112.txt">Table of n, a(n) for n = 0..10000</a>

%e 101 contains two 1s and one 0, therefore a(101) = 2110;

%e 102 contains one 2, one 1 and one 0, therefore a(102) = 121110.

%t f[n_] := Block[{s = Split@ IntegerDigits@ n}, FromDigits@ Reverse@ Riffle[Union@ Flatten@ s, Length@# & /@ s]]; Array[f, 48, 0] (* _Robert G. Wilson v_, Dec 01 2016 *)

%o (Haskell)

%o import Data.List (sort, group); import Data.Function (on)

%o a244112 :: Integer -> Integer

%o a244112 n = read $ concat $

%o    zipWith ((++) `on` show) (map length xs) (map head xs)

%o    where xs = group $ reverse $ sort $ map (read . return) $ show n

%o (Python)

%o def A244112(n):

%o     return int(''.join([str(str(n).count(d))+d for d in '9876543210' if str(n).count(d) > 0])) # _Chai Wah Wu_, Dec 01 2016

%o (PARI) A244112(n,c=1,S="")={for(i=2,#n=vecsort(digits(n),,4),n[i]==n[i-1]&&c++&&next;S=Str(S,c,n[i-1]);c=1);eval(Str(S,c,if(n,n[#n])))} \\ _M. F. Hasler_, Feb 25 2018

%Y Cf. A047842, A010785.

%Y See A036058 for the orbit of 0 under this map.

%K nonn,base

%O 0,1

%A _Reinhard Zumkeller_, Nov 11 2014