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A260526
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.
3
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, 21, 21, 21, 21, 12, 12, 12, 12, 21, 21, 21, 21, 21, 21, 12, 12, 12, 12, 12, 21, 21, 21, 21, 21, 12, 12, 12, 12, 12, 12, 21, 21, 21, 21, 12, 12, 12, 12, 12, 12, 12, 21, 21
OFFSET
0,11
COMMENTS
Sequence A260274 lists fixed points of this function.
Sequence A260519 is the same except for concatenating a 0 for digits which do not occur.
EXAMPLE
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.
PROG
(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)}
CROSSREFS
Cf. A260527 - A260529 and A260519 - A260522 for variants; A045918 for the classical "look and say" sequence.
Sequence in context: A372219 A064161 A260528 * A040133 A092538 A354571
KEYWORD
nonn,base
AUTHOR
M. F. Hasler, Jul 28 2015
STATUS
approved