A216589 Numbers n which don't have a preimage for A216556, i.e., such that A216587(n)=-1.

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

Offset: 1

Author

M. F. Hasler, Sep 09 2012

Keywords

• nonn
• base
• easy

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

• E. Angelini, Strings resurrection, SeqFan mailing list, Sep 08 2012

Programs

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))}

Formula

A216587(n)=-1 if and only if n is in this sequence.