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%I #12 Jun 17 2021 04:38:41
%S 1000000000,100000000,10000000,1000000,100000,10000,1000,100,10,1,
%T 2100000000,1200000000,120000000,102000000,100200000,100020000,
%U 100002000,100000200,100000020,100000002,2010000000,210000000,120000000,12000000,10200000,10020000,10002000,10000200,10000020,10000002
%N Concatenate the positions of digits 0, 1, ..., 9 in the decimal representation of n, using 1 for the leftmost digit etc., and 0 when the digit does not occur.
%e Consider n=1103: the digit '0' is at the 3rd position, digit '1' in the 1st and 2nd places, digit '2' does not occur, digit '3' at the 4th position, digits 4-9 do not occur. Thus a(1103) = 31204000000.
%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));p=concat(p);p[1]=Str(p[1]);eval(concat(p))}
%Y Cf. A260519, A260521 and A260522 for variants.
%Y Cf. A045918 for the classical "look and say" sequence.
%K nonn,base
%O 0,1
%A _M. F. Hasler_, Jul 28 2015
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