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 A321804 Keep only consecutive identical decimal digits of n; write -1 if all digits disappear. 2
 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 22, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 33, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 44, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 55, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 66, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 77, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 88, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 99, 0, -1, -1, -1, -1, -1, -1, -1, -1, -1, 11, 111, 11, 11, 11, 11, 11, 11, 11, 11, -1, -1, 22, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 33, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 44, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 55, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 66, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 77, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 88, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 99 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,12 COMMENTS Consecutive identical digits of n are kept. Leading zeros are erased unless the result is 0. If all digits are erased, we write -1 for the result (A321803 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 A321800 for n < 121. LINKS EXAMPLE 123321 becomes 33, 1123 becomes 11, 112331 becomes 1133, and 100223 becomes 22 (as we don't accept leading zeros). Note that 12321 disappears immediately and we get -1. MATHEMATICA Array[If[# == {}, -1, FromDigits@ #] &@ Apply[Join, Select[Split@ IntegerDigits[#], Length@ # > 1 &]] &, 200] (* Michael De Vlieger, Nov 23 2018 *) PROG (Python) from re import split def A321804(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)) CROSSREFS Cf. A320486, A321800, A321797, A321800, A321803. Sequence in context: A337335 A109014 A268357 * A321800 A130837 A010194 Adjacent sequences:  A321801 A321802 A321803 * A321805 A321806 A321807 KEYWORD sign,base AUTHOR Chai Wah Wu, Nov 19 2018 STATUS approved

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Last modified September 27 03:21 EDT 2020. Contains 337380 sequences. (Running on oeis4.)