A260526 - OEIS

%I #5 Jul 28 2015 12:45:08

%S 1,1,1,1,1,1,1,1,1,1,12,12,21,21,21,21,21,21,21,21,12,12,12,21,21,21,

%T 21,21,21,21,12,12,12,12,21,21,21,21,21,21,12,12,12,12,12,21,21,21,21,

%U 21,12,12,12,12,12,12,21,21,21,21,12,12,12,12,12,12,12,21,21

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

%C Sequence A260274 lists fixed points of this function.

%C Sequence A260519 is the same except for concatenating a 0 for digits which do 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 '3' at 1st position, digits 2 and 4-9 do not occur. Thus a(1103) = 2341.

%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));if(1<#p=concat(select(t->#t,p)),p[1]=Str(p[1]);eval(concat(p)),p)}

%Y Cf. A260527 - A260529 and A260519 - A260522 for variants; A045918 for the classical "look and say" sequence.

%K nonn,base

%O 0,11

%A _M. F. Hasler_, Jul 28 2015