OFFSET
0,3
COMMENTS
Consecutive identical digits of n are erased. Leading zeros are erased unless the result is 0. If all digits are erased, we write -1 for the result (A321801 is another version, which uses 0 for the empty string).
More than the usual number of terms are shown in order to reach some interesting examples. Agrees with A320485 for n < 101.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 0..10000
EXAMPLE
12311 becomes 123, 1123 becomes 23, 11231 becomes 231, and 110232 becomes 232 (as we don't accept leading zeros). Note that 112233 disappears immediately and we get -1.
1110 becomes 0 and 11000, 1100011 all become -1.
MATHEMATICA
A321802[n_]:=With[{d=Flatten[Select[Split[IntegerDigits[n]], Length[#]==1&]]}, If[d=={}, -1, FromDigits[d]]]; Array[A321802, 100, 0] (* Paolo Xausa, Nov 14 2023 *)
PROG
(Python)
from re import split
def A321802(n):
return (lambda x: int(x) if x != '' else -1)(''.join(d if len(d) == 1 else '' for d in split('(0+)|(1+)|(2+)|(3+)|(4+)|(5+)|(6+)|(7+)|(8+)|(9+)', str(n)) if d != '' and d != None))
(PARI) apply( A321802(n)={if(n, forstep(i=#n=digits(n), 2, -1, n[i]!=n[i-1]&&next; if(i<3||n[i-2]!=n[i], n=n[^i]; i--); n=n[^i]); if(#n, fromdigits(n), -1))}, [0..122]) \\ M. F. Hasler, Nov 20 2018
CROSSREFS
KEYWORD
sign,base
AUTHOR
Chai Wah Wu, Nov 19 2018
STATUS
approved