A260519 - OEIS

%I #7 Jul 28 2015 12:44:26

%S 1000000000,100000000,10000000,1000000,100000,10000,1000,100,10,1,

%T 1200000000,1200000000,210000000,201000000,200100000,200010000,

%U 200001000,200000100,200000010,200000001,1020000000,120000000,120000000,21000000,20100000,20010000,20001000,20000100,20000010,20000001

%N Concatenate the positions of digits 0, 1,..., 9 in the decimal representation of n, using 1 for the rightmost digit etc., and 0 when the digit does not occur.

%e Consider n=1103, the digit '0' is at 2nd position (looking from the right), digit '1' in 3rd and 4th place, digit '2' does not occur, digit '3' at 1st position, digits 4-9 do not occur. Thus a(1103) = 23401000000.

%o (PARI) a(n)={my(p=vector(10));for(i=1,#n=if(n,Vecrev(digits(n)),[0]),p[n[i]+1]=if(p[n[i]+1],concat(p[n[i]+1],i),i));p=concat(p);p[1]=Str(p[1]);eval(concat(p))}

%Y Cf. A260520 - A260522 for variants; A045918 for the classical "look and say" sequence.

%K nonn,base

%O 0,1

%A _M. F. Hasler_, Jul 28 2015