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%I #7 Jul 28 2015 12:45:27
%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
%N Concatenate the positions of digits 9, 8,..., 0 in the decimal representation of n, using 1 for the leftmost digit etc., skip digits which don't occur.
%e Consider n=1103: the digit '3' is at the 4th position (looking from the left), digit '1' is in 1st and 2nd place, digit '0' is at 3rd position, digits 2 and 4-9 do not occur. Thus a(1103) = 4123.
%o (PARI) a(n)={my(p=vector(10));for(i=1,#n=if(n,digits(n),[0]),p[n[i]+1]=if(p[n[i]+1],concat(p[n[i]+1],i),i));if(1<#p=concat(Vecrev(select(t->#t,p))),p[1]=Str(p[1]);eval(concat(p)),p)}
%Y Cf. A260526 - 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
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