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 A216589 Numbers n which don't have a preimage for A216556, i.e., such that A216587(n)=-1. 3
 0, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Concretely, numbers having "20", "30", ..., "90" or "00" as a substring, or starting with "11", "12", ... "19", and the number 0. Note that A216557 does not necessarily yield 0 for these numbers, e.g., 10 has no preimage for A216556, but 210 does have, and 10 -> 21 -> ... -> 98 -> 109. LINKS Table of n, a(n) for n=1..58. E. Angelini, Strings resurrection, SeqFan mailing list, Sep 08 2012 FORMULA A216587(n)=-1 if and only if n is in this sequence. PROG (PARI) is_A216589(n)={n || return(1); n=Vec(Str(n)); n[1]<"2" & 1<#n & n[2]>"0" & return(1); for(i=2, #n, n[i]=="0" || next; n[i-1]=="1" || return(1))} CROSSREFS Sequence in context: A270036 A178405 A162903 * A038687 A359983 A236403 Adjacent sequences: A216586 A216587 A216588 * A216590 A216591 A216592 KEYWORD nonn,base,easy AUTHOR M. F. Hasler, Sep 09 2012 STATUS approved

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Last modified December 4 22:39 EST 2023. Contains 367565 sequences. (Running on oeis4.)